anisotropy in the indian ocean upper mantle from rayleigh and love waveform inversion a tomographic method is applied to love and rayleigh wave seismograms in order to address the problem of upper mantle elastic anisotropy in the indian ocean the first step in our approach is a waveform inversion for each path of the study a 1 d depth dependent model compatible with the waveforms of the fundamental mode and several higher modes of love and rayleigh waves is obtained then the models related to the different paths are inverted in order to retrieve 3 d velocity heterogeneities and anisotropy in this paper both the radial anisotropy and the azimuthal anisotropy of s waves are investigated in detail we find a significant radial anisotropy in the uppermost 300 km of the mantle with an overall amplitude smaller than what is found in global studies azimuthal s wave anisotropy is also present the directions of fast s velocities show rather simple patterns from 100 to 300 km depth and strong correlations with the direction of absolute plate motion apm are found in the uppermost 100 km the pattern of fast velocity directions is complex and does not correlate simply with plate motions from 100 to 200 km depth a correlation with apm is found in most oceanic regions the main lack of correlation is located in the vicinity of la reunion and mauritius islands in this region the anisotropy exhibits a complex pattern between 100 and 150 km possibly due to a disturbing effect of the hotspot at 200 km depth and deeper azimuthal anisotropy vanishes progressively beneath most of the oceanic regions no significant azimuthal anisotropy is found beyond 300 km depth the depth extent of both azimuthal and radial anisotropy the amplitude of radial anisotropy and the pattern of azimuthal anisotropy support the idea of a preferential orientation of olivine crystals in a low viscosity zone beneath the lithosphere this region would be located between 100 and 200 km in oceanic areas and possibly deeper between 200 and 300 km in continental areas not well resolved in this study

orbital forcing of organic carbon burial in the proto north atlantic during oceanic anoxic event 2 the cenomanian turonian c t intervals at dsdp sites 105 and 603b from the northern part of the proto north atlantic show high amplitude short term cyclic variations in total organic carbon toc content the more pronounced changes in toc are also reflected by changes in lithology from green claystones toc 1 although their depositional history was different the individual toc cycles at sites 105 and 603b can be correlated using stable carbon isotope stratigraphy sedimentation rates obtained from the isotope stratigraphy and spectral analyses indicate that these cycles were predominately precession controlled the coinciding variations in hi oi 13corg and the abundance of marine relative to terrestrial biomarkers as well as the low abundance of lignin pyrolysis products generated from the kerogen of the black claystones indicate that these cyclic variations reflect changes in the contribution of marine organic matter om the cooccurrence of lamination enrichment of redox sensitive trace metals and presence of molecular fossils of pigments from green sulfur bacteria indicate that the northern proto north atlantic ocean water column was periodically euxinic from the bottom to at least the base of the photic zone 150 m during the deposition of the black claystones in contrast the green claystones are bioturbated are enriched in mn do not show enrichments in redox sensitive trace metals and show biomarker distributions indicative of long oxygen exposure times indicating more oxic water conditions at the same time there is evidence e g abundance of biogenic silica and significant 13c enrichment for oc of phytoplanktic origin for enhanced primary productivity during the deposition of the black claystones we propose that increased primary productivity periodically overwhelmed the oxic om remineralisation potential of the bottom waters resulting in the deposition of om rich black claystones because the amount of oxygen used for om remineralisation exceeded the amount supplied by diffusion and deep water circulation the northern proto north atlantic became euxinic during these periods both sites 105 and 603b show trends of continually increasing toc contents and hi values of the black claystones up section which most likely resulted from both enhanced preservation due to increased anoxia and increased production of marine om during oceanic anoxic event 2 oae2

nearshore euxinia in the photic zone of an ancient sea part ii the bigger picture and implications for understanding ocean anoxia abstract biomarker palaeontological and isotopic evidence suggests that the late permian carbonate seas i e the northern npb and southern spb permian basins of northern pangea were characterized by significant spatial and temporal variations in the palaeowater column redox state this is particularly the case with regard to the deposition of the lopingian zechstein cycle 2 carbonate rocks a shelf to basin reconstruction of environmental conditions was achieved by analysing nearly 400 core samples from 49 wells this allowed an evaluation of the spatial variations in facies and broad oceanographic conditions at the basin scale specifically in the lower slope and shallow basin facies of the northern margin of the spb present day northern poland and eastern germany highly variable concentrations of the green sulphur bacterial biomarkers chlorobactane and isorenieratane and their likely degradation products c 15 to c 31 2 3 6 aryl isoprenoids indicative of photic zone euxinia and homohopane indices indicative of anoxia combined with the presence of a benthic fauna and bioturbation indicate a variable but occasionally anoxic euxinic water column locally in lagoonal facies in the northern and southern margin of the spb euxinic conditions also developed but these were likely associated with localised conditions or benthic production in association with microbialites the presence of gammacerane in the eastern spb south eastern germany and eastern poland suggests elevated salinities there compatible with the restricted configuration of the basin however a lack of these signatures in basinal settings of the eastern spb indicates that strongly reducing conditions were restricted to the lower slope and shallow basin locations and restricted lagoons and were not developed in the basin centre moreover this anoxia euxinia in marginal settings is restricted to the north eastern part of the spb the south eastern part of the spb se poland in contrast is devoid of evidence for pze the southern margin of the spb is also characterized by generally oxic suboxic conditions with local anoxia limited to more restricted embayments and elevated salinities limited to restricted oxic anoxic lagoons in the western spb ne england and adjacent offshore and the npb outer moray firth offshore scotland the water columns were oxic suboxic overall it appears that high but episodic primary bioproductivity of organic matter was concentrated on or even limited to the lower slopes of the spb s north eastern margin and the restricted lagoons and shallow basin of its southern margin leading to the formation of source rocks for petroleum in these areas in addition the temporal and geographical restriction of anoxia appears to have prevented the accumulation of large and more widespread quantities of organic matter in fact toc contents exhibit a poor correlation with ecological and anoxia indicators crucially this work confirms that the strong evidence for pze observed in shelf and lower slope shallow basin facies of the north eastern spb need not be associated with widespread basin scale anoxia this conclusion has implications for organic matter burial carbon cycling and biotic crises during other times in earth history

global anisotropy in the upper mantle inferred from the regionalization of phase velocities a data set of 2600 paths for rayleigh waves and 2170 paths for love waves was selected in order to resolve azimuthal anisotropy of surface waves in the period range 70 250 s the epicenters were chosen so that the paths provide uniform spatial and azimuthal coverage of earth a synthetic seismogram is computed for each path and compared to the observed seismogram in order to infer the phase velocity along each path to process such a large data set a new tomographic technique is designed a good correlation is found with surface tectonics in the whole period range for love waves and at shorter periods for rayleigh waves the directions of maximum velocities are also well correlated with plate tectonics motions for the 2 azimuthal term of rayleigh waves when the power spectrum of heterogeneities is computed it is found that for love waves the even orders are usually larger than the odd orders for rayleigh waves the degrees 2 and 6 dominate only at long periods suggesting a deep origin for these components

active hydrothermal discharge on the submarine aeolian arc 1 in november 2007 we conducted a water column and seafloor mapping study of the submarine volcanoes of the aeolian arc in the southern tyrrhenian sea aboard the r v urania on 26 conductivity temperature depth casts and tows we measured temperature conductivity pressure and light scattering and also collected discrete samples for helium isotopes methane and ph the 3he 4he isotope ratio an unambiguous indicator of hydrothermal input showed a clear excess above background at 6 of the 10 submarine volcanoes surveyed marsili seamount had the highest anomaly where the 3he 4he ratio reached a 3he value of 23 at 610 m depth compared with background values of 5 smaller but distinct 3he anomalies occurred over palinuro enarete eolo sisifo and secca del capo although hydrothermal emissions are known to occur offshore of some aeolian subaerial volcanoes and hydrothermal deposits have been sampled throughout the arc our results are the first to confirm active discharge on marsili enarete eolo sisifo and secca del capo samples collected over lametini filicudi north alicudi north and alcione had 3he near the regional background values suggesting either absence of or very weak hydrothermal activity on these seamounts hydrocasts between the volcanoes revealed a consistent 3he maximum between 11 and 13 at 2000 m depth throughout the se tyrrhenian sea the volcanoes of the aeolian arc and the marsili back arc all 1000 m deep cannot contribute directly to this maximum this deep 3he excess may be a remnant of tritium decay or may have been produced by an unknown deep hydrothermal source

the backus gilbert approach to the three dimensional structure in the upper mantle i lateral variation of surface wave phase velocity with its error and resolution summary the backus gilbert method is applied to obtain the phase velocity variations on a sphere from the measured phase velocity narrow peak kernels with radii of about 2000 km are obtained for almost everywhere on the sphere the phase velocity results are thus interpreted as an average within such regions the most trouble comes from the antipodal peak in the resolution kernel this is evaluated as contamination and is incorporated in the error estimation the total error which is a root mean square of contamination from the antipodal peak and statistical error estimated from the data covariance matrix is about 1 per cent of the phase velocity in the average earth model which is the preliminary reference earth model prem however there is about a factor of 2 variation of errors on the sphere maximum variations of phase velocity are about 3 4 per cent of the phase velocity in the average earth model and thus there still remain anomalies which exceed estimated errors the estimated errors correspond to one standard deviation under the assumptions of uncorrelated gaussian distribution for high confidence interval they show that statistically significant anomalies are scarce for the current data set generally love wave phase velocity maps show more resolved features than rayleigh wave maps and we can see in high confidence maps fast velocities in old oceans and old continents and slow velocities in tectonically active regions like the east pacific rise and various back arc regions

the sapropel record of the eastern mediterranean sea results of ocean drilling program leg 160 research on sediments recovered during ocean drilling leg 160 has concentrated on two issues the first concerned the stratigraphy of sapropel formation the second was oriented to clarify specific processes that explain sapropel origin progress has been made in the construction of stratigraphic composites out of sedimentary sequences from individual holes at each of the palaeoceanographic sites on the composites initial work has resulted in the establishment of high resolution and intermediate resolution stratigraphies for three sites 963 964 967 correlation of sedimentary cycles to astronomical insolation cycles extends the stratigraphies to sites 969 and 966 the sapropel occurrences in the marine and land sequences over the entire eastern mediterranean are correlated with the resolution that can be obtained from isotope studies groups of sapropels occurred simultaneously over the entire basin in detail however the temporal and facies patterns of sapropel sequences differ between individual sites and depositional basins the differences may be related to effects of water depth diagenesis and post depositional tectonic attenuation of sequences studies on the geochemistry and facies of sapropels agree that anoxic conditions favoured preservation of organic matter in sapropels caused the enrichment of trace metals associated with sapropels and helped to preserve primary sedimentary structures besides all evidence is consistent with elevated fluxes of organic matter and associated elements during sapropel events

stable isotopic evidence for climate and basin evolution of the late cretaceous songliao basin china abstract because of the need to understand the links and feedbacks of the carbon cycle during times of global greenhouse conditions numerous studies have focused on the cretaceous climate much of what we know about this warm period in earth s history comes from the study of ocean sediments recovered from both ocean drill cores and marine sediments exposed at the earth s surface in contrast there are few studies of cretaceous terrestrial sediments the songliao basin located in northeast china offers a unique opportunity to understand cretaceous paleoclimate of terrestrial settings because it contains a nearly complete record of lacustrine sediments deposited throughout the cretaceous and there is an active drilling program to recover core from this paleolake we present carbon oxygen and strontium isotopic data from ostracods collected from two drill cores sk 1 n and sk 1 s that cover a time interval that extends from the turonian through the maastrichtian these data record robust isotopic trends with numerous carbon and oxygen isotope shifts that are both rapid and long term we tentatively interpret this record to reflect changes in both global climate and regional basin evolution in the turonian and coniacian qingshankou formation we observe several carbon isotope shifts that appear to be correlative to marine isotopic records based upon timing and magnitude of the isotopic changes we suggest that the carbon isotope record in the songliao basin reflect the decrease in carbon isotope ratios following the strong positive excursion at the cenomanian turonian boundary a positive isotope excursion in the late turonian and the negative isotope shift that occurs at the turonian coniacian boundary upward in the section however the marine and songliao isotopic records diverge as sediment sources shift from the southwest east and north to more northerly strontium isotopes record the change in source region as they increase markedly between the coniacian santonian yaojia and santonian campanian nenjiang formations as this is the first isotopic record of the songliao basin we are cautious about many of our interpretations of these isotopic data yet it is clear that with tighter age constraints and focused sampling centered on many of the isotope excursions presented here will allow for a deeper understanding of the terrestrial response to changing climate and the hydrologic response to basin evolution

complete archive of late turonian to early campanian sedimentary deposition in newly drilled cores from the tarfaya basin sw morocco an expanded succession of organic rich marlstones and limestones deposited in the tarfaya basin provides an outstanding opportunity to closely retrace climate evolution and sea level changes during the cretaceous greenhouse period we present high resolution x ray fluorescence xrf scanning and bulk carbon and oxygen isotope records from two newly drilled sediment cores in the tarfaya atlantic coastal basin which recovered a continuous upper turonian to campanian succession of 290 m thickness the xrf core scanning records reveal three long term oscillations in the abundance of terrigenous elements increase of al ti k si and fe normalized against ca which correspond to progressive transgressive phases followed by rapid regressions during the coniacian and early santonian sea level highstands during this interval corresponding to the coniacian santonian oceanic anoxic event 3 oae 3 are characterized by overall oxygen depleted to anoxic conditions at the seafloor indicated by the high organic carbon content the presence of laminations and low log mn s high log v ca and high log br ca the upper santonian interval marks the transition from anoxic to oxic bottom water conditions prevalent through the early campanian the composite bulk carbonate 13 c curve exhibits strong similarities to the global stacked 13 c reference curve characterized by negative excursions in the early coniacian navigation and east cliff events and late santonian bracketed by the haven brow and buckle events and by positive excursions in the latest turonian hitchwood event middle coniacian wight fall event and at the santonian campanian boundary during the early campanian enhanced accumulation of fine grained carbonate and clay rich hemipelagic sediments increasing bulk carbonate 18 o and low log br ca and log v ca values indicate climate cooling associated with a substantial improvement in bottom water ventilation two long term 13 c cycles of 2 m y duration probably related to variations in earth s orbital eccentricity are associated with the long term cooling trend initiating the campanian maastrichtian climate transition toward a cool greenhouse state

a record of long and short term environmental and climatic change during oae3 la luna formation late cretaceous santonian early campanian venezuela abstract the la luna formation was deposited under anoxic dysoxic conditions in a tropical epicontinental sea on the northwest south america margin sedimentological micropaleontological and geochemical evidence provides insights into factors that influenced the sedimentation and controlled the accumulation of organic rich deposits at decimeter and meter scales during the youngest of the cretaceous oceanic anoxic events oae the la luna formation consists of an alternation of black marlstones interbedded with black limestones and black marly limestones the benthic foraminifera assemblages indicate sedimentation in the upper neritic to upper bathyal environment these rocks contain large amounts of organic matter it is interpreted that a combination of warm global and rainy climate and the presence of bathymetric barriers caused poor circulation and low rates of water column ventilation during a high sea level in the early santonian leading to the preservation of carbon rich deposits in this region during the late santonian a cooling trend in global climate increased wind strength and upwelling this change probably reduced runoff causing a weakening of the pycnocline and destabilized the stratification in the water column providing a progressive increase in oxygen in the water column and on the sea floor and a decrease in total organic carbon preservation in a shallower basin these changes and the establishment of full mid and deep water exchange in response to the deepening and widening of the equatorial atlantic gateway could have been important mechanisms for ending the epeiric sea anoxia changes through time in the vanadium nickel fraction planktonic and benthic foraminifera assemblages productivity proxy elements and lithological characteristics support this model superimposed on the general trend variations in calcium carbonate and total organic carbon percentages at the scale of tens of centimeters reveal high frequency cyclic variations which apparently correspond to the main frequencies of orbital forcing this cyclicity is interpreted as a primary depositional signal and is the result of orbital controlled fluctuations in terrigenous dilution and variations in oxygen concentration at the base of the water column variations in the intensity of upwelling can be observed but they did not control the cyclicity

mechanism of backarc opening in the japan sea role of asthenospheric injection abstract the process of backarc extension in the japan sea includes two modes of spreading the parallel and rotational or fan shape opening data from paleomagnetism for rocks on the northeast japan arc radiometric age determination for dredged volcanic rocks and heat flow in the basin have suggested that the parallel opening of the japan sea took place earlier than the rotational opening at 21 14 ma the mechanism of opening of the japan sea has been examined based on the secular change in the geometry of the subducted slab and in the volcanic activity on the northeast japan arc mechanisms of backarc rifting including mantle diapirism mantle flow induced by the slab subduction or interaction of the over and the underriding plates cannot reasonably explain the process of opening of the japan sea the most plausible mechanism operating in the spreading process of the japan sea is injection of the asthenosphere into the mantle wedge that forcefully pushed the subducted slab to cause both steepening of the slab and the backarc extension the asthenospheric current towards the northeast japan arc trench system may have been associated with the large scale upwelling of the asthenosphere beneath the northeastern china region that caused intra plate volcanism and produced continental rift systems in the region the present mechanism can also explain the active backarc rifting in the okinawa trough in the western pacific and the taupo depression in north island new zealand

late cretaceous dysoxia in a southern high latitude siliciclastic succession the otway basin southeastern australia the warm greenhouse world of the late cretaceous created oceans that were poorly stratified latitudinally and vertically periodically these oceans experienced globally significant events where oxygen minimum zones enveloped the continental margins evidence of the effect of one of these ocean anoxic events oaes is preserved in the southern high latitude strata of the offshore otway basin in southeast australia during the late cretaceous thick successions up to 6 km of mudstonedominated deltaic to upper bathyal sediments the otway delta were deposited in an elongate inlet ca 500 km wide between antarctica and australia located at least 708 s the initial turonian strata of this succession the waarre formation were deposited in upper delta plain to delta front conditions the overlying late turonian flaxman formation and basal belfast mudstone formation preserve evidence of transgressive lower delta plain to prodelta conditions at inner to middle shelf depths these units were subject to periodic dysoxia during deposition caused by intermittent freshwater input and deepening seas resulting in periods of thermohaline stratification and reduced bottom waters rapid subsidence from 89 3 ma to 85 7 ma created significant accommodation space leading to the seaward progradation of normal marine prodelta to upper bathyal mudstone dominated facies at middle shelf to upper slope depths after a period when the oxygen minimum zone contracted near the base of the coniacian upward increasing dysoxia in the belfast mudstone formation heralds the onset of coniacian to santonian dysoxic conditions this event in the otway basin correlates to oae 3 the last ocean anoxic event of the warm cretaceous before the onset of cooler conditions in the uppermost cretaceous the evidence suggests that rather than confined to low latitude tropical areas the effects of oae 3 reached southern high latitude regions during the warm late cretaceous the cessation of growth faulting after 85 7 ma reduced accommodation space and delta front to prodelta facies prograded rapidly seaward hyposaline conditions and higher sedimentation rates due to delta front progradation and shallowing during this time

lithospheric shear wave velocity and radial anisotropy beneath the northern part of north china from surface wave dispersion analysis rayleigh and love wave phase velocities in the northern part of the north china are obtained from ambient noise tomography in the period range of 8 35 s and two plane wave earthquake tomography at periods of 20 91 s using data recorded at 222 broadband seismic stations from the temporary north china seismic array and permanent china digital seismic array the dispersion curves of rayleigh and love wave from 8 to 91 s are jointly inverted for the 3 d shear wave structure and radial anisotropy in the lithosphere to 140 km depth distinct seismic structures is observed from the fenhe graben and taihang mountain to the north china basin the north china basin from the lower crust to the depth of 140 km is characterized by high velocity anomaly reflecting mafic intrusion and residual materials after the extraction of melt and by strong radial anisotropy with vsh vsv implying horizontal layering of intrusion and alignment of minerals due to vigorous extensional deformation and subsequent thermal annealing however low velocity anomaly and positive radial anisotropy are observed in the fenhe graben and taihang mountain suggesting the presence of partial melt in the lithosphere due to the mantle upwelling and horizontal flow pull

crustal structure beneath ne china imaged by necessarray receiver function data abstract we analyzed tens of thousands of receiver function data recorded by 185 broadband seismic stations to study the crustal structure beneath the northeast china moho depth and average crustal v p v s ratio were measured at each station using the h grid searching technique for stations located above unconsolidated sediments we applied the h method to remove strong shallow reverberations and generate subsurface receiver functions that allow for effective h analysis the measurements show that the songliao basin has a relatively thin crust 31 km and the moho depth increases significantly from southeast 27 km to northwest 35 km the northwestward tilting of the songliao basin may suggest that it was initiated by lithospheric flexure due to the load of the great xing an range in the jurassic before the large scale extension in the cretaceous moho depth varies from 26 7 km to 42 3 km across the study area with the shallowest and deepest moho being located at the eastern flank of the songliao basin and the great xing an range respectively the moho depth correlates well with the surface topography in the western part but not the central and eastern parts of the study area the residual topography computed based on the airy s isostasy model indicates that the high topography at the eastern flank of the songliao basin the changbaishan volcanic center and the southern end of the great xing an range is likely dynamically supported by the upper mantle

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

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

late cretaceous to early quaternary organic sedimentation in the eastern equatorial atlantic abstract reconstructing the long term evolution of organic sedimentation in the eastern equatorial atlantic odp leg 159 provides information about the history of the climate ocean system sediment accumulation and deposition of hydrocarbon prone rocks the recovery of a continuous 1200 m long sequence at odp site 959 covering sediments from albian to the present day about 120 ma makes this position a key location to study these aspects in a tropical oceanic setting new high resolution carbon and pyrolysis records identify three main periods of enhanced organic carbon accumulation in the eastern tropical atlantic i e the late cretaceous the eocene oligocene and the pliocene pleistocene formation of upper cretaceous black shales off west africa was closely related to the tectono sedimentary evolution of the semi isolated deep ivorian basin north of the cote d ivoire ghana transform margin their deposition was confined to certain intervals of the last two cretaceous anoxic events the early turonian oae2 and the coniacian santonian oae3 organic geochemical characteristics of laminated coniacian santonian shales reveal peak organic carbon concentrations of up to 17 and kerogen type i ii organic matter which qualify them as excellent hydrocarbon source rocks similar to those reported from other marginal and deep sea basins a middle to late eocene high productivity period occurred off equatorial west africa porcellanites deposited during that interval show enhanced total organic carbon toc accumulation and a good hydrocarbon potential associated with oil prone kerogen deposition of these toc rich beds was likely related to a reversal in the deep water circulation in the adjacent sierra leone basin accordingly outflow of old deep waters of southern ocean origin from the sierra leone basin into the northern gulf of guinea favored upwelling of nutrient enriched waters and simultaneously enhanced the preservation potential of sedimentary organic matter along the west african continental margin a pronounced cyclicity in the carbon record of oligocene lower miocene diatomite chalk interbeds indicates orbital forcing of paleoceanographic conditions in the eastern equatorial atlantic since the oligocene miocene transition a similar control may date back to the early oligocene but has to be confirmed by further studies latest miocene early pliocene organic carbon deposition was closely linked to the evolution of the african trade winds continental upwelling in the eastern equatorial atlantic ocean chemistry and eustatic sea level fluctuations reduction in carbonate carbon preservation associated with enhanced carbon dissolution is recorded in the uppermost miocene 5 82 5 2 ma section and suggests that the latest miocene carbon record of site 959 documents the influence of corrosive deep waters which formed in response to the messinian salinity crisis furthermore sea level related displacement of higher productive areas towards the west african shelf edge is indicated at 5 65 5 6 5 55 5 2 4 8 ma in view of humid conditions in tropical africa and a strong west african monsoonal system around the miocene pliocene transition the onset of pronounced toc cycles at about 5 6 ma marks the first establishment of upwelling cycles in the northern gulf of guinea an amplification in organic carbon deposition at 3 3 ma and 2 45 ma links organic sedimentation in the tropical eastern equatorial atlantic to the main steps of northern hemisphere glaciation and testifies to the late pliocene transition from humid to arid conditions in central and western african climate aridification of central africa around 2 8 ma is not clearly recorded at site 959 however decreased and highly fluctuating carbonate carbon concentrations are observed from 2 85 ma on that may relate to enhanced terrigenous eolian dilution from africa

seismic evidence of on going sublithosphere upper mantle convection for intra plate volcanism in northeast china abstract a 3 d crustal and upper mantle s wave velocity model of ne china is constructed by inversion of phase velocity dispersion curves at 6 140 s periods from ambient noise tomography and two plane surface wave tomography the seismic data used in this study are collected from 120 china earthquake administration cea permanent stations and 127 portable stations of necessarray we observe strong low s wave velocity beneath the changbaishan volcano in the upper mantle to at least 200 km depth which is interpreted as a mantle upwelling beneath the changbaishan volcano that is consistent with the body wave tomographic image the songliao basin is dominated by a high velocity extending to at least 200 km depth built upon the observed velocity anomalies we propose a sub lithosphere mantle convection model for ne china in which the upwelling of upper mantle materials from the mantle transition zone to the changbaishan volcano could induce a local sub lithosphere convection in the upper mantle and the strong high velocity of the upper mantle beneath the songliao basin corresponds to the downwelling limb of this convection cell the downwelling beneath the songliao basin could also induce secondary local convection in the asthenosphere to the west leading to local asthenospheric upwelling beneath the abaga and halaha volcanoes in the xing an mongolia orogenic belt

mapping convection in the mantle long period 100 250 sec love and rayleigh waves are used to map heterogeneity and azimuthal anisotropy in the upper mantle spherical harmonic descriptions of anisotropy up to l m 3 and 2 are derived azimuthal anisotropy obtains values as high as 1 there is good correlation of fast rayleigh wave directions with upper mantle return flow directions derived from kinematic considerations this is consistent with the a axis of olivine being aligned in the flow direction the main differences between the flow models and the rayleigh wave azimuthal variation maps occur in the vicinity of hotspots hawaii for example appears to perturb the return flow there is strong correlation of the geoid and surface wave velocity at l 4 and 5 slow regions at this scale are associated with geoid highs and high heat flow consistent with upwelling convective flow or with isostatically compensated regions of low density the correlation of azimuthal anisotropy with upper mantle return flow directions rather than with plate directions suggests that part of the return flow is in the upper mantle and this in turn implies a low viscosity channel

insolation control on the late cretaceous hydrological cycle and tropical african climate global climate modelling linked to marine climate records data from late cretaceous paleoclimate simulations and their linkage to a geological model derived from long term high resolution proxy data indicate and support strong relationships between african climate and tropical atlantic sedimentation here we present results from an interdisciplinary study by varying only one parameter in the set of orbital boundary conditions of the numeric model we focus on the climatic impact of precessional forcing on the global and regional climate system as a result new insights to the internal dynamics of climate the different compartments and fluxes of the hydrological cycle and finally the sedimentary response within the oceanic realm during greenhouse conditions have been approached the climate models suggest that insolation changes at 25 55 s are the trigger for cyclic variations of the tropical hydrological cycle of northern africa between the various models a maximum difference in insolation at the top of the atmosphere of 14 w m2 is needed to produce the documented changes in the hydrological cycle first of all the simulations do not suggest any substantial latitudinal movement of the itcz over the course of one precessional cycle the models rather indicate cross latitudinal variation of pressure systems and variation in the magnitude and direction of surface winds linking tropical africa to the mid southern latitudes this cross latitudinal atmospheric teleconnection denotes a reduced role of the tropics as driver of cretaceous climate system therefore the linkage of proxy based geological and numeric models rather supports the idea that tropical atlantic black shale formation in the late cretaceous was ultimately triggered by climate change in mid southern latitudes with precipitation and river discharge being the transport mechanisms as a hypothesis that will be tested in the near future we speculate that the mid latitudes represent the ultimate region of climate signal formation during times of extreme global warmth

millennial to centennial scale record of african climate variability and organic carbon accumulation in the coniacian santonian eastern tropical atlantic ocean drilling program site 959 off ivory coast and ghana millennial to centennial scale geochemical records of coniacian to santonian deposits from the deep ivorian basin are used to develop a model for the accumulation of black shales in equatorial regions during the final of the cretaceous oceanic anoxic events oae proxy records from ocean drilling program site 959 document a strong precessional signal in the occurrence of black shales the abundance of quartz and clay mineralogy during oae 3 we hypothesize that this signal reflects changes in atmospheric circulation patterns which in turn caused latitudinal shifts of continental climate belts across western africa furthermore we propose that the periodic deposition of black shales occurred in response to adjustments of oceanic circulation in the deep ivorian basin resulting from climate controlled fluctuations in continental runoff a new high resolution cyclostratigraphic framework allowed us to estimate a rapid change within 1000 yr from dysoxic background to anoxic or euxinic black shale environmental conditions followed by black shale deposition for 10 k y and a gradual return to the initial dysoxic conditions our findings imply a highly dynamic late cretaceous atmosphere ocean system

facies architecture and high resolution sequence stratigraphy of an upper cretaceous platform margin succession southern central pyrenees spain abstract excellent exposures of upper cretaceous santonian carbonate platforms on the northern flank of sant corneli anticline southern central pyrenees provide detailed information of facies architecture in both depositional strike and dip directions basic accretional units are differentiated by facies contrast across mappable surfaces these surfaces do not show clear evidence of subaerial erosion and are correlated basinward with bedding planes across which there are subtle changes in skeletal composition two types of basic accretional units have been identified based on bedding patterns internal facies architecture and skeletal composition 1 rudist buildups consist of a rudist and coral belt at the platform margin passing landward into a slender hippuritid lithosome locally overlain by a bioclastic blanket that passes basinward into bioclastic apron like clinobeds and into fine grained packstone wackestone 2 calcarenite wedges consist of yellow brown benthic foraminifer rich grainstones to grain dominated packstones with scattered rudist shells and small coral colonies passing basinward into mud dominated packstones to wackestones with variable siliciclastic content quartz sand to silt and clay rudist buildups and calcarenite wedges alternate although not rhythmically these changes in platform skeletal composition reflect changes in the dominant type of carbonate producing biota independently of the changes in accommodation both types of basic accretional units rudist buildups and calcarenite wedges form simple sequences and parasequences according to internal lithofacies arrangement and inferred sea level cyclicity cycles or paracycles high frequency sea level cyclicity fits in the milankovitch frequency band long term changes in accommodation governing aggradation progradation and backstepping of basic sequences and parasequences reflect tectonic influence rather than long term changes in eustatic sea level

stability of the astronomical frequencies over the earth s history for paleoclimate studies the expected changes over the past 500 million years in the principal astronomical frequencies influencing the earth s climate may be strong enough to be detectable in the geological records and such effects have been inferred in several cases calculations suggest that the shortening of the earth moon distance and of the length of the day back in time induced a shortening of the fundamental periods for the obliquity and climatic precession from 54 to 35 41 to 29 23 to 19 and 19 to 16 thousand years over the last half billion years at the same time the precessional constant increased from 50 to 61 arc seconds per year the changes in the frequencies of the planetary system due to its chaotic motion are much smaller their influence on the changes of the periods of climatic precession obliquity and eccentricity of the earth s orbit around the sun can be neglected eccentricity periods used for quaternary climate studies may therefore be considered to have been more or less constant for pre quaternary times

cenomanian to campanian carbon isotope chemostratigraphy from the western interior basin u s a abstract late cretaceous carbon isotope curves generated for localities in europe asia and the deep sea records have provided the foundation for development of a contiguous intercontinental chemostratigraphic framework despite the development of carbon isotope records from selected stratigraphic intervals in the western interior basin however a comprehensive 13c record comparable to those developed in europe and asia and from odp sites had not yet been completed this study reports a new high resolution cenomanian to campanian carbon isotope record for the central western interior basin of north america that makes a key contribution to the intercontinental correlation the curve is correlated to the well developed molluscan biostratigraphic framework for the western interior basin as well as a revised geochronology based on integration of new radioisotopic dating and astrochronology developed in the same core records from where the 13c data were derived the new 13c record reflects not only major perturbations in the global carbon cycle such as the mid cenomanian event and the cenomanian turonian ocean anoxic event 2 but also smaller excursions that have been recognized in records from europe and asia this shows that the western interior shallow epeiric sea was not isolated for any appreciable part of cenomanian to early campanian time it consistently recorded changes in the global marine carbon cycle observed elsewhere a critical attribute of the chemostratigraphic dataset produced in this study is its linkage with a revised late cretaceous time scale assignment of revised ages to western interior carbon isotope events that are globally expressed will allow export of the improved time scale to localities within and outside the western interior where similar carbon isotope records have been generated this chronostratigraphic tool will allow a number of stratigraphic and geochemical hypotheses to be more rigorously tested

crustal and upper mantle structure of southeast tibet from rayleigh wave tomography 1 we have applied the two plane wave inversion technique to fundamental mode rayleigh waves in southeast tibet phase velocity variations are obtained at 15 periods from 20 to 143 s and are used to construct three dimensional shear wave velocity structure a low velocity zone is imaged in the middle crust of southeast tibet in which velocity perturbation varies from 4 to 3 the slow area might be associated with high temperature and partial melt and can flow ductilely while the high velocity region could be relatively cold and mechanically strong enough to pass crustal strain implying that coherent lithospheric deformation is possible with the presence of complicated crustal flow strong negative anomalies in the shallow crust are imaged at 92 e correlating with the location of a north south rift zone a fast mantle lid to a depth of 120 km is present beneath most of the study area the lithosphere is significantly slower in the central part of the study area than in the west and east to the east of 96 e a subvertical high velocity zone is imaged at 120 240 km depths under the bangong nujiang suture bns which is more like the subduction of the asian lithosphere we interpret the high velocity anomalies to the south of the bns as the subducted indian lithosphere and those to the north as the asian lithosphere a vertical low velocity column is observed in the central part of the region from the lower crust to the midupper mantle which is probably in part responsible for the rift at 92 e the slow anomaly is likely associated with asthenosphere upwelling following the opening of a slab window that could have developed when the slab was torn apart vertically because of the significant change of subducting direction at the eastern syntaxis

warm tropical ocean surface and global anoxia during the mid cretaceous period the middle of the cretaceous period about 120 to 80 myr ago was a time of unusually warm polar temperatures1 repeated reef drowning in the tropics2 and a series of oceanic anoxic events oaes that promoted both the widespread deposition of organic carbon rich marine sediments and high biological turnover3 4 5 6 7 8 the cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide7 8 9 10 11 12 in contrast there is no consensus on the climatic causes and effects of the oaes with both high biological productivity and ocean stagnation being invoked as the cause of ocean anoxia3 4 5 6 7 8 here we show using stable isotope records from multiple species of well preserved foraminifera that the thermal structure of surface waters in the western tropical atlantic ocean underwent pronounced variability about 100 myr ago with maximum sea surface temperatures 3 5 c warmer than today this variability culminated in a collapse of upper ocean stratification during oae 1d the breistroffer event a globally significant period of organic carbon burial that we show to have fundamental stratigraphically valuable geochemical similarities to the main oaes of the mesozoic era our records are consistent with greenhouse forcing being responsible for the warm temperatures but are inconsistent both with explanations for oaes based on ocean stagnation and with the traditional view reviewed in ref 12 that past warm periods were more stable than today s climate

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

itcz controls on late cretaceous black shale sedimentation in the tropical atlantic ocean 1 this study presents high resolution organic and inorganic proxy records for coniacian to santonian black shale on the demerara rise odp site 1261 in the western tropical atlantic off south america we integrate these records with approximately time equivalent geochemical data from the eastern tropical atlantic off tropical africa odp site 959 to extract the underlying relationships of intertropical convergence zone itcz dynamics and black shale formation in the tropical cretaceous atlantic at orbital time scales the geochemical records from the demerara rise show repetitive fluctuations in productivity ocean redox conditions and clastic sediment supply consistent with a dynamic paleo upwelling regime off tropical south america upwelling intensity most likely was driven by shifts of the mean annual position of the itcz which connects the large scale precipitation and wind field patterns of the hadley cells upwelling was strongest off south america and burial of oil prone organic matter most pronounced when the itcz was in its southernmost position which maximized the impact of ne trade winds on the inner tropical part of the northern hadley cell geochemical records from the deep ivorian basin equatorial atlantic suggest that source rock formation occurred in phase with regions north of the equator off tropical africa however black shale formation was primarily driven by regional rainfall and nutrient export the results of this study provide a conceptual framework that explains the formation distribution and quality of petroleum source rocks below the tropical component of the hadley cells on orbital time scales

high resolution 3 d crustal structure beneath ne china from joint inversion of ambient noise and receiver functions using necessarray data abstract we used ambient noise data recorded by the necessarray a portable seismic array deployed in northeast china to construct rayleigh wave phase velocity dispersion curves and obtain phase velocity maps for periods from 6 to 40 s s wave velocity structure beneath ne china is obtained by joint inversion of the phase velocities and receiver functions our results show good correlation between crustal velocity structure and geological features at shallow depths the songliao basin is separated into two small sub basins by a fast velocity anomaly corresponding to a southwest uplifted horst and the southern sub basin is associated with the kailu depression a low velocity anomaly extending from the lower crust to uppermost mantle beneath the changbaishan mountain range is consistent with p and s wave tomography models the mantle low velocity has been interpreted as a local mantle upwelling attributed to the subducting pacific slab induced return flow finally the s wave velocity in the mid and lower crust is lower beneath the xing an mongolia orogenic belt xmob than beneath the changbaishan mountain range this was not expected since the changbaishan mountain range has experienced more extensive volcanic activity in the cenozoic including the currently active changbaishan and jingpohu volcanoes than the xmob we infer that the mid and lower crust of the xmob is mainly felsic in composition and propose that the low shear wave velocity of the mid and lower crust beneath the xmob could be the consequence of removal of deep mafic crust through a continental accretion and subsequent delamination event in the paleozoic or via convection removal induced by the rollback of the flat subducted paleo pacific slab during the middle mesozoic

marine black shale deposition and hadley cell dynamics a conceptual framework for the cretaceous atlantic ocean understanding the controls that determine the spatial distribution and internal heterogeneities of black shales in the mesozoic ocean has been a focal point of research over many decades the consensus is that atmosphere land ocean interactions influenced variations in marine biogeochemistry and sediment supply thus exerting fundamental controls on the richness and quality of sedimentary organic matter om and ultimately on petroleum source rock distribution and its generation potential internal small scale heterogeneities in black shales that have been reported from all ocean settings were often linked to orbitally driven fluctuations in continental runoff and marine upwelling the two processes are generically related under the ascending tropical and descending subtropical limbs of the palaeo hadley cells with fluctuations at variable time seasonal orbital geological and spatial shelf margin deep basin scales these dynamic variations translate into characteristic patterns of om quantity and quality best preserved near the continents where the forcing effects are strongest the expression of these orbital scale interactions are not well constrained at the basin scale however they may hold a key to better understand the distribution of heterogeneities in black shales this study presents a conceptual framework that links om quality and quantity in cretaceous atlantic sediments with the dominant processes that operated under the hadley cells using a comprehensive compilation of bulk organic geochemical data total organic carbon concentration toc hydrogen index hi oxygen index oi and kerogen type we explore how basic geochemical patterns can be used to identify the underlying generic processes we utilise published and new data from deep ocean sites of the dsdp odp program as well as one palaeo shelf setting tarfaya spanning a latitudinal transect from the outer subtropics to the palaeo equator during the albian the cenomanian turonian and the coniacian santonian this study emphasises the potential of integrating orbital scale datasets and wide spatial coverage as a predictive tool for black shale formation across ocean basins

radial anisotropy beneath northeast tibet implications for lithosphere deformation at a restraining bend in the kunlun fault and its vicinity three dimensional shear wave velocity and radial anisotropy models of the crust and upper mantle beneath the ne tibetan plateau are constructed from new measurements of love wave dispersions 20 77s and previously obtained rayleigh wave dispersions 20 87s using a two plane wave method the mid lower crust is characterized with positive anisotropy vsh vsv with large strength beneath the qinling and qilian mountains and small values beneath the anyemaqen mountain the large positive anisotropy can be explained by horizontal alignment of anisotropic minerals in the mid lower crust due to crustal flow the mantle lithosphere above 90 km is largely isotropic while weak positive anisotropy appears beneath 90 km which probably marks the lithosphere asthenosphere boundary lab a low shear wave velocity anomaly and relatively negative radial anisotropy are imaged in the entire lithosphere beneath the restraining bend in the eastern kunlun fault consistent with a weak lithosphere experiencing vertical thickening under horizontal compression the asthenosphere at the restraining bend is characterized by significant low velocity and positive radial anisotropy reflecting that the asthenosphere here is probably hotter has more melts and deforms more easily than the surrounding region we propose that the lithosphere at the restraining bend was vertically thickened and subsequently delaminated locally and induced asthenosphere upwelling this model explains the observations of velocity and anisotropy anomalies in the lithosphere and asthenosphere as well as geological observations of rapid rock uplift at the restraining bend of the kunlun fault

origin of intraplate volcanism in northeast china from love wave constraints the tectonic source for widespread volcanism in northeast china has not been completely understood we develop a 3 d sh velocity model in ne china that provides new constraints to the origin of the volcanism the 3 d model is constructed from fundamental mode love waves at the periods of 20 125 s recorded at 269 broadband seismic stations the changbai mountain is characterized by a significant low velocity in the lower crust and uppermost mantle which probably results from mantle upwelling due to the subduction of the pacific plate a fast and thin mantle lid of 75 km is present beneath the songliao basin indicating lithosphere extension from back arc rifting the slow velocity in the middle and fast velocities in the south and north at 75 115 km depths in the songliao basin suggest complex mantle flow with upwelling and downwelling unlike the other volcanic fields changbaishan volcano jingpohu volcano and abaga volcano the halaha volcano has high velocity in the lower crust and upper mantle implying a limited melt supply from mantle source recently the subduction induced upwelling leads to complicated small scale mantle convection which is responsible for the intraplate magmatism in northeast china

euxinia and primary production in late cretaceous eastern equatorial atlantic surface waters fostered orbitally driven formation of marine black shales 1 oceanic anoxic events oae in the cretaceous represent major perturbations in the global climate and ocean system characterized by widespread deposition of organic carbon in the ocean the causes and effects of these events are poorly constrained mainly because of the lack of high resolution marine records here we report the distribution of molecular markers from a millennial scale record of coniacian santonian black shale oae 3 from ocean drilling program site 959 in the deep ivorian basin in the eastern equatorial atlantic highly branched isoprenoids and alkenone derived organic compounds indicate that diatoms and calcareous nanoplankton were important primary producers changes in redox sensitive trace metal accumulation and biomarkers of green sulfur bacteria provide evidence for extreme variations in redox conditions with intervals of lower photic zone euxinia pze accordingly oxygen in the coniacian santonian tropical atlantic was absent as during the cenomanian turonian boundary oae 2 but over more restricted geographic area and more limited time intervals we hypothesize that pze was a common phenomenon typical in large areas of tropical continental margins these conditions fostered sequestration of atmospheric co2 and thus helped cause the positive excursion in 13c of carbonate documented in higher latitude marine records

redox sensitivity of p cycling during marine black shale formation dynamics of sulfidic and anoxic non sulfidic bottom waters abstract a high resolution geochemical record of a 120 cm black shale interval deposited during the coniacian santonian oceanic anoxic event 3 odp leg 207 site 1261 demerara rise has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo redox conditions high contents of organic matter sulfur and redox sensitive trace metals cd mo v zn as well as continuous lamination point to deposition under consistently oxygen free and largely sulfidic bottom water conditions however rapid and cyclic changes in deep ocean redox are documented by short term 15 20 ka intervals with decreased total organic carbon toc s and redox sensitive trace metal contents and in particular pronounced phosphorus peaks up to 2 5 wt p associated with elevated fe oxide contents sequential iron and phosphate extractions confirm that p is dominantly bound to iron oxides and incorporated into authigenic apatite preservation of this fe p coupling in an otherwise sulfidic depositional environment as indicated by fe speciation and high amounts of sulfurized organic matter may be unexpected and provides evidence for temporarily non sulfidic bottom waters however there is no evidence for deposition under oxic conditions instead sulfidic conditions were punctuated by periods of anoxic non sulfidic bottom waters during these periods phosphate was effectively scavenged during precipitation of iron oxyhydr oxides in the upper water column and was subsequently deposited and largely preserved at the sea floor after 15 25 ka sulfidic bottom water conditions were re established leading to the initial precipitation of cds zns and pyrite subsequently increasing concentrations of h2s in the water column led to extensive formation of sulfurized organic matter which effectively scavenged particle reactive mo complexes thiomolybdates at site 1261 sulfidic bottom waters lasted for 90 100 ka followed by another period of anoxic non sulfidic conditions lasting for 15 20 ka the observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface to mid waters from the south atlantic resulting in a lowering of the oxic anoxic chemocline in the water column alternatively sea water sulfate might have been stripped by long lasting high rates of sulfate reduction removing the ultimate source for hs production

astrochronology of the late turonian implications for the behavior of the carbon cycle at the demise of peak greenhouse abstract a series of prominent carbon cycle perturbations indicated by carbon isotope excursions of up to 2 marked climatic and oceanographic changes that followed the peak mid cretaceous greenhouse the nature and forcing mechanisms of these changes remain poorly understood partly due to the lack of a detailed temporal control in this interval here we present an orbitally calibrated time scale which is based on hemipelagic rhythmites in the bohemian cretaceous basin and which can be linked to the established chronostratigraphic framework using inoceramid biostratigraphy and carbon isotope signature in the new age model the late turonian defined by the first occurrence of i perplexus below and the first occurrence of c deformis erectus above spans 1 56 0 07 myr when anchored to the newly refined age of the turonian coniacian boundary sageman et al in press the onset of the late turonian is 91 31 0 45 ma inoceramid zones i perplexus and m scupini span 0 76 0 05 myr and 0 80 0 05 myr respectively a time domain record of carbon isotope variations was obtained by pinning published 13ccarb data to the orbital time scale using 9 biostratigraphic and carbon isotope markers the timing of major carbon isotope excursions suggests a link to 405 kyr eccentricity changes and in the early late turonian to 100 kyr eccentricity variations however over 80 of the variance in the late turonian 13 c occurs at longer million year scales the key features of the 13ccarb signature including the amplified long term variance can be reproduced with simple models of orbitally driven isotopic mass balance at a constant carbon isotope fractionation the best fit to the 13ccarb signature is obtained with enhanced organic burial at high eccentricity in accordance with monsoonal forcing of organic accumulation in the low latitude atlantic and or buildup of low latitude terrestrial carbon reservoirs alternative solutions should consider changing carbon isotope fractionation due to pco2 and or nutrient flux changes

chemostratigraphic resolution of widespread reducing conditions in the southwest pacific ocean during the late paleocene abstract paleogene strata throughout much of the southwest pacific is comprised of thick successions of fine grained siliceous to calcareous sediments however during the late paleocene the south pacific experienced widespread deposition of organic rich and 13corg enriched sediments that are recorded in the waipawa formation and the correlative waipawa organofacies the mechanisms responsible for the elevated input and preservation of organic matter are still poorly understood using a multi proxy chemostratigraphic approach we assess paleoceanographic conditions including paleo redox states and paleo productivity of the waipawa formation eight key sections from the east coast basin new zealand were sampled and analysed for multi element geochemistry and bulk pyrolysis sedimentological stratigraphic and chemostratigraphic evidence indicates the south pacific underwent an abrupt regression event during the late paleocene resulting in on shelf erosion and or bypassing of continental sourced sediments from the shelf into deeper waters the change in sediment delivery further increased nutrients and terrestrial organic matter loading to the site of deposition coeval excursions in ti zr and rb sr indicate a shift to an aluminosilicate dominated sediment supply resulting in a modest increase in marine productivity that cannot account for the anomalous organic matter enrichment changes in the hydrogen index show a transition from terrestrial to mixed terrestrial marine organic matter occurred during the late paleocene in which high concentration of type ii iii kerogens were buried and preserved in association with enhanced water column reducing conditions in deep marine settings elevated concentrations of redox sensitive trace elements e g u mo fe s are consistent with alternating phases of dysoxic to oxic conditions suggesting an expansion of an oxygen minimum zone enhancing preservation and delivery of organic matter to the seafloor leading to the subsequent burial and preservation of organic matter within anoxic sediments these new data provide insight into the depositional conditions and the petroleum potential of prospective source rocks in this basin using an integrated organic and inorganic geochemical approach to refine our knowledge of the depositional environment and paleoceanographic changes in shelfal to bathyal marine sediments of the late paleocene

late mesozoic calc alkaline volcanism of post orogenic extension in the northern da hinggan mountains northeastern china abstract late mesozoic calc alkaline volcanism in the northern da hinggan mountains ndhm ne china exhibits geochemical and sr nd isotopic characteristics similar to those of cenozoic calc alkaline volcanism in the basin and range province usa whole rock k ar dating results show that these volcanic sequences were erupted during 138 116 ma composed of basaltic andesites trachyandesites group 1 hornblende andesites trachytes group 2 and rhyolite lavas group 3 they are characterized by low mgo contents 4 20 lile lree enrichment and significant nb ta depletion as well as a little depleted to slightly enriched nd and weakly enriched sr isotopic ratios group 1 initial 87sr 86sr 0 70502 0 70572 nd t 0 78 to 0 91 group 2 initial 87sr 86sr 0 70497 0 70518 nd t 0 86 to 1 26 group 3 initial 87sr 86sr 0 70510 0 70635 nd t 0 41 to 0 25 the systematic variations in major and trace elements homogeneous sr nd isotope data and temporal consistency among three volcanic groups indicate that they were derived from a similar mantle source metasomatized by fluids related to the closure of the paleo asian and or mongolia okhotsk oceans and were produced through different degrees of fractional crystallization of the primary melts group 1 basaltic rocks were formed through removal of olivine and pyroxene of the primary melts while group 2 trachytes which contain the lowest lree contents e g la 24 28 ppm and relatively less enriched sr and higher nd isotope ratios were generated after removal of a few percent of lree rich minerals such as hornblende clinopyroxene and apatite of melts like group 1 group 3 rhyolite lavas exhibiting the highest abundances of strongly incompatible elements such as rb and k moderate lree contents e g la 28 53 ppm as well as apparently negative eu and sr anomalies represent the final crystallized products following a plagioclase predominant fractionation of melts like group 2 the low mgo contents and evolved affinities of the volcanic rocks imply that beneath the ndhm there existed many crustal magma reservoirs throughout the eruption episodes in which mantle derived primary melts had experienced intense differentiation these facts in combination with the contemporaneous basin and range tectonic regime suggest that the extensive calc alkaline volcanism in the ndhm was attributed to post orogenic diffuse extension rather than either an upwelling mantle plume or mesozoic oceanic plate subduction

paleoceanographic and paleoclimatic similarities between mediterranean sapropels and cretaceous black shales pliocene quaternary sapropels of the mediterranean sea and mid cretaceous black shales share many distinctive properties organic carbon concentrations that often exceed 5 in both types of sequences record episodes of exceptional accumulation of organic matter although both are rich in marine organic matter they have high c n ratios that mimic those of land plant organic matter which suggests less efficient organic matter recycling than in the modern ocean the coupled presence of isorenieratene derivatives and low 15n values that result from microbial primary productivity indicates that photic zone anoxia existed during their formation and implies strong stratification of the surface ocean enrichments of redox sensitive metals and sediment laminations indicate that anoxia existed deeper in the water column and at the seafloor multiple proxies indicate freshening of surface waters of the mediterranean and imply periods of wetter climate during times of sapropel deposition episodes of black shale deposition similarly coincide with times of wetter climate these comparisons suggest that the wetter climate created similar conditions of surface salinity stratification that enhanced microbial primary production and magnified organic matter export during deposition of both the mediterranean sapropels and mid cretaceous black shales

sh wave structure of the crust and upper mantle in southeastern margin of the tibetan plateau from teleseismic love wave tomography abstract the deep structure of southeastern tibet is important for determining lateral plateau expansion mechanisms such as movement of rigid crustal blocks along large strike slip faults continuous deformation or the eastward crustal channel flow we invert for 3 d isotropic sh wave velocity model of the crust and upper mantle to the depth of 110 km from love wave phase velocity data using a best fitting average model as the starting model the 3 d sh velocity model presented here is the first sh wave velocity structure in the study area in the model the tibetan plateau is characterized by prominent slow sh wave velocity with channel like geometry along strike slip faults in the upper crust and as broad zones in the lower crust indicating block like and distributed deformation at different depth positive radial anisotropy vsh vsv is suggested by a high sh wave and low sv wave anomaly at the depths of 70 110 km beneath the northern indochina block this positive radial anisotropy could result from the horizontal alignment of anisotropic minerals caused by lithospheric extensional deformation due to the slab rollback of the australian plate beneath the sumatra trench

s wave velocity structure of northeastern china from joint inversion of rayleigh wave phase and group velocities summary we imaged the crust and uppermost mantle structure beneath northeastern ne china with fundamental mode rayleigh waves recorded by 125 broad band stations deployed in the region rayleigh wave phase and group velocities along more than 700 interstation paths were estimated using the wavelet transformation method and then these data were utilized to construct 2 d phase and group velocity maps in the period range of 15 60 s owing to the dense ray coverage and short ray path our results provide better lateral resolution in the ne china region compared with previous phase and group velocity studies the regularized rayleigh wave phase and group velocity dispersions at each cell were jointly inverted to determine 1 d shear wave velocity structure using the linear inversion method and then assembled into a 3 d model our results show that obvious low velocities exist in the uppermost mantle beneath the changbaishan volcanic region which may be due to asthenospheric upwelling the thin lithosphere with fast s wave velocity in the lower crust of the songliao basin implies that the lithospheric mantle beneath ne china is partly removed

constraining p wave velocity variations in the upper mantle beneath southeast asia we have produced a p wave model of the upper mantle beneath southeast se asia from reprocessed short period international seismological centre isc p and pp data short period p data of the annual bulletin of chinese earthquakes abce and long period pp p data we used 3d sensitivity kernels to combine the datasets and mantle structure was parameterized with an irregular grid in the best sampled region our data resolve structure on scale lengths less than 150 km the smearing of crustal anomalies to larger depths is reduced by a crustal correction using an a priori 3d model our tomographic inversions reveal high velocity roots beneath the archean ordos plateau the sichuan basin and other continental blocks in se asia beneath the himalayan block we detect high seismic velocities which we associate with subduction of indian lithospheric mantle this structure is visible above the 410 km discontinuity and may not connect to the remnant of the neo tethys oceanic slab in the lower mantle our images suggest that only the southwestern part of the tibetan plateau is underlain by indian lithosphere and thus that the upper mantle beneath northeastern tibet is primarily of asian origin our imaging also reveals a large scale high velocity structure in the transition zone beneath the yangtze craton which could have been produced in multiple subduction episodes the low p wave velocities beneath the hainan island are most prominent in the upper mantle and transition zone they may represent counter flow from the surrounding subduction zones and may not be unrelated to processes beneath eastern tibet 2005 elsevier b v all rights reserved

cenozoic episodic volcanism and continental rifting in northeast china and possible link to japan sea development as revealed from k ar geochronology abstract cenozoic volcanic rocks in northeast china comprise part of the volcanic belt of the western circum pacific rim and represent one of the presently active tectono magmatic regions of the world over 590 volcanoes with erupted basalts covering an area of 50 000 km 2 are exposed in the songliao graben and particularly on its flanks k ar dating of the volcanic rocks sampled from a selection of eruption sites over the region reveals that the volcanism occurred episodically through the entire cenozoic corresponding to the tectono magmatic interactions particularly between the india eurasia and pacific plates the volcanism initiated in the songliao graben in late cretaceous 86 ma and migrated flankward since 28 ma the magmatic propagation shows three major stages intimately associated with the evolution of japan sea and related to the geodynamic forcing of the india eurasia collision prior to japan sea rifting volcanic eruptions were restricted to the songliao basin during japan sea opening volcanism migrated into the lateral belts after cessation of japan sea opening at 15 ma volcanism with greatest intensity occurred on both flanks particularly along the yi yi fault system around 14 13 ma and subsequently the fu mi fault between 11 and 7 ma continuing this trend of migration eruptions scattered further away from the songliao basin in the last 4 5 ma we suggest that the cenozoic volcanic belt in northeast china and the japan sea backarc basin are competitive parts in the eastern marginal magmatic system of the eurasian plate the early stage of the volcanism in the songliao basin may have resulted from mantle upwelling beneath the songliao bohai basin belt rifting of the ne faults and relatively weak intensity of volcanism in northeast china during japan sea opening could be attributable to the lithospheric breakup in the japan sea and spreading of japan sea the subsequent strong volcanism in northeast china after cessation of the japan sea opening implicates the easiest pathway for the melts of the magmatic system in the plate margin the diversified volcanism in scattered localities during the quaternary may indicate localized melting processes or notable modifications in smaller sized individual domains and possibly a magmatically waning phase of the limited source in eastern china

changbaishan volcanism in northeast china linked to subduction induced mantle upwelling the changbaishan volcanic complex in china cannot be easily explained as the consequence of a mantle plume seismic images from the region identify buoyant mantle material that may have been entrained and dragged downwards by the subducting pacific plate but is now escaping upwards through a gap in the plate and producing the intraplate volcanism

40ar 39ar and k ar dating on the volcanic rocks in the songliao basin ne china constraints on stratigraphy and basin dynamics precise 40ar 39ar and k ar ages were determined on sanidine and whole rock separates of volcanic rocks in the songliao basin sb the volcanism is characterized by a series of continual and episodic eruptions in the late jurassic 147 157 ma and early cretaceous 113 136 ma a fairly accurate chronostratigraphic column was first established based on those data the volcanic activities happened synchronously with closure of the mongolia okhotsk ocean north to the sb structures of the volcanogenic successions are s dipping or se dipping fault blocks coupled with n dipping or nw dipping major detachment systems distribution of the volcanics revealed by high resolution seismic reflections is neither restricted within nor in agreement with the framework of the overlying sedimentary sequence striking nne this new evidence fits the overlap model proposed in the present paper that formation of the volcanic successions in the sb is related to the subduction of the mongolia okhotsk plate under the mongolia north china block during the jurassic and early cretaceous whereas the overlying sedimentary sequence unconformably on the volcanics is tectonically controlled by the oblique subduction of the pacific plate under the eurasian plate since late aptian in addition the coal bearing epiclastic sediments intercalating the volcanics were deposited at the subduction quiescence episodes when extensional collapse occurred

20 my of nitrogen fixation during deposition of mid cretaceous black shales on the demerara rise equatorial atlantic ocean abstract thick sequences of dark colored organic carbon rich finely laminated santonian cenomanian claystones and homogeneous albian siltstones were recovered from ocean drilling program sites 1257 1258 and 1260 on the demerara rise in the western equatorial atlantic ocean total organic carbon toc concentrations vary from 2 to over 20 wt in the sequences of black shales that were deposited over a period of 20 million years similarly long periods of elevated marine productivity implied by the high toc concentrations are uncommon in the geological record and must have required unusual paleoceanographic conditions the importance of nitrogen fixing bacteria to sustaining the amplified export production of organic matter is indicated by 15n values that remain between 4 and 0 a range that is notably less positive than the average of 5 for modern ocean sediments although containing mostly marine organic matter the black shales have toc tn molar ratios between 20 and 40 that mimic those of land plant organic matter the anomalously large toc tn ratios suggest selective organic matter degradation probably associated with low oxygen conditions in the water column that favored preservation of nitrogen poor forms of organic matter relative to nitrogen rich components deposition of black shales on the demerara rise was likely a consequence of the mid cretaceous warm and wet greenhouse climate that strengthened thermohaline stratification of this part of the atlantic ocean which in turn encouraged bacterial nitrogen fixation enhanced primary production magnified organic matter export and ultimately established anoxic conditions at the seafloor that improved preservation of organic matter for much of the 20 my period represented by these thick sequences

the geodynamic evolution of the eastern eurasian margin in mesozoic times abstract the cenozoic features of eurasia such as marginal seas and intracontinental deformation are unraveled using available paleomagnetic and field data the late cretaceous shape of eurasia is then reconstructed from the examples of sw japan and south russian far east the major features of the mesozoic eurasian margin suture zones marked by ophiolites or high pressure metamorphic rocks olistostromes characterized by the lithology of the olistoliths calc alkaline magmatism and strike slip faults are outlined correlations of the ophiolitic belts and the olistostromes along the eastern eurasian margin from borneo to siberia allow the definition of four microcontinents the west philippines south japan and the anuy and okhotsk sea microblocks from south to north the mesozoic structure of the eurasian margin is due to three processes 1 1 oceanic subduction and the accretion of subduction complexes 2 2 the collision of these microcontinents with eurasia between the late jurassic and the late cretaceous and 3 3 the reactivation of the ophiolitic sutures by left lateral wrench faulting

evolution of tropical watersheds and continental hydrology during the late cretaceous greenhouse impact on marine carbon burial and possible implications for the future abstract regional climate modelling for the late cretaceous greenhouse and high resolution marine stratigraphic records from both sides of the low latitude atlantic show that tropical south american and african hydrology and watersheds had a strong effect on freshwater transfer into the equatorial atlantic and subsequently the marine carbon record this conclusion is derived from new detailed geochemical records from demerara rise off suriname drilled at ocean drilling program odp site 1261 combined with frequency analyses and climate simulations providing evidence for mainly eccentricity driven changes in carbon burial in the western tropical atlantic shorter orbital frequencies in particular precession clearly dominating black shale cycles off tropical africa odp site 959 are far less dominant at demerara rise despite comparable time resolution of the geochemical records we suggest that these different frequency patterns in carbon burial were related to the regional evolution of cretaceous watersheds and hydrology in tropical south america and africa river discharge deduced from simulations indicates higher and less variable discharge from south america compared to western africa at that time this runoff pattern would have supported more permanent anoxic conditions off south america compared to africa at least indirectly and caused the lack of strong higher frequency geochemical cycles in the western sector of the equatorial atlantic furthermore climate simulations show a general switch of primary runoff from either side of the cretaceous equatorial atlantic every half precession cycle i e every 10 kyr similarities between the developments of cretaceous and holocene hydrology in the tropical atlantic area imply that orbital scale evolution of watersheds is a robust feature through time that is independent from the mean global climate state based upon the comparison of cretaceous and holocene trends in hydrology we infer that future hydrology in the study region may develop in a comparable direction to the one observed in the cretaceous if true this suggests that the modern amazon rain forest could shrink over the next millennium due to a 30 loss of moisture while the congo rain forest in africa is likely to expand in response to a 14 gain in moisture

orbital forcing of triassic megamonsoon activity documented in lacustrine sediments from ordos basin china abstract the hothouse triassic climate provides a key window to study megamonsoon systems however high quality paleoclimate proxy records are rarely reported from the tethys realm where the seasonal meridional migration of the intertropical convergence zone itcz should be the most remarkable here continuous and well dated proxy records are used to study monsoon activity in the northeastern tethys from the middle triassic lacustrine sediments ch7 black shale yanchang formation in the ordos basin china the proxies including natural gamma ray intensity magnetic susceptibility and element concentrations and ratios u k zr al zr rb and sr rb document a strong precession signal in the sediments we propose that the periodic deposition of the ch7 black shale occurred in response to intensifications in a monsoon driven climate enhanced by the early ladinian warming event climate variability in the ordos basin 25 n reflects the harmonics of 100 kyr 20 kyr and 10 kyr cycles and is highly coherent with solar insolation at 9 latitude suggesting that this monsoon system might have been modulated by tropical solar insolation the dominance of tropical climate processes in this mid latitude monsoon region can be attributed to the dramatic dynamics of the itcz and intense monsoon circulation in the tethys realm

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

crustal and lithospheric structure of northeast china from s wave receiver functions abstract lithospheric thickness is closely associated with lithospheric response to tectonic forces or thermal processes analysis of s wave receiver functions srfs from a dense seismic array has revealed lithospheric thickness variations along a 1200 km long profile that spans all major geological terranes of northeast china the srf images identify the shallowest moho and lithosphere asthenosphere boundary lab depths beneath the rifted songliao basin thus spatially correlating well with the thick sediment accumulation these features can be explained by a pure shear regime operating in the lower crust and upper mantle suggesting the predominance of roughly symmetric lithosphere stretching from continental rifting in contrast thicker lithosphere in western and eastern terranes of ne china indicates the lithosphere in these regions was not strongly affected by the extensional processes during the late mesozoic flat lab structure beneath the erguna and xing an terranes along with the overlying relatively deeper moho beneath the great xing an range suggests the north south gravity lineament may not be a trans lithospheric structure

jiggling the tropical thermostat in the cretaceous hothouse modern open ocean sea surface temperatures rarely exceed 28 29 8c and the same has been thought to represent a rough maximum for past tropical climates however new isotopic estimates from the uppermost cenomanian in the tropical western north atlantic suggest that mixed layer temperatures reached 33 34 8 c 62 8c during the middle cretaceous hothouse uppermost cenomanian tropical sea surface temperatures may have been as much as 4 7 8c warmer than the highest modern mean annual temperatures such extreme conditions suggest that warm tropical oceans could have driven substantially intensified atmospheric heat transport near the cenomanian turonian boundary the tropical thermostat was set higher than today challenging the hypothesis of tropical climate stability

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

organic geochemical characterization of santonian to early campanian organic matter rich marls sondage no 1 cores as related to oae3 from the tarfaya basin morocco abstract in addition to previously analyzed sediments of cenomanian to santonian age in the tarfaya sondage no 2 well this study presents the results of a stratigraphically younger interval of santonian to early campanian age in the adjacent well tarfaya sondage no 1 this interval is part of the oceanic anoxic event 3 oae3 which occurred mainly in the atlantic realm due to known high quality source rocks related to oaes i e cenomanian turonian the investigated sample section was tested for the quality quantity and kind of organic matter om describing also the depositional environment the study was carried out by means of i elemental analysis c org caco 3 ts ii rock eval pyrolysis iii vitrinite reflectance measurements iv gas chromatography flame ionization detection gc fid and v gc mass spectrometry gc ms total content of organic carbon c org values for the hydrogen index hi mainly in the range 500 700 mg g c org and s 2 values 10 40 mg g rock support the assumption of a high petroleum generation potential in these upper cretaceous sediments ts c org ratios as well as pristane phytane ratios indicate variable oxygen contents during sediment deposition representing a typical depositional setting for the late cretaceous and are in good agreement with previously analyzed data in the tarfaya basin phyto and zoo plankton were identified as marine sourced all of the investigated early campanian and santonian samples are immature with some tendencies to early maturation these results are based on vitrinite reflectance 0 3 0 4 vr r t max values 409 425 c production indices pi s 1 s 1 s 2 n alkane ratios i e carbon preference index as the deposition of these sediments is time related to oae3 the depositional environment was characterized by oxygen deficiency or even anoxic bottom water conditions this situation was favored during the cretaceous greenhouse climate by limited oxygen solubility in the then warmer ocean water furthermore local factors related to nutrient supply and primary bioproductivity led to the exceptionally thick upper cretaceous organic matter rich sedimentary sequence of the tarfaya basin

consequences of moderate 25 000 yr lasting emission of light co 2 into the mid cretaceous ocean future warming is predicted to shift the earth system into a mode with progressive increase and vigour of extreme climate events possibly stimulating other mechanisms that invigorate global warming this study provides new data and modelling investigating climatic consequences and biogeochemical feedbacks that happened in a warmer world not vert similar 112 myr ago our study focuses on the cretaceous oceanic anoxic event oae 1b and explores how the earth system responded to a moderate not vert similar 25 000 yr lasting climate perturbation that is modelled to be less than 1 c in global average temperature using a new chronological model for oae 1b we present high resolution elemental and bulk carbon isotope records from dsdp site 545 from mazagan plateau off nw africa and combine this information with a coupled atmosphere land ocean model the simulations suggest that a perturbation at the onset of oae 1b caused almost instantaneous warming of the atmosphere on the order of 0 3 c followed by a longer not vert similar 45 000 yr period of not vert similar 0 8 c cooling the marine records from dsdp site 545 support that these moderate swings in global climate had immediate consequences for african continental supply of mineral matter and nutrients phosphorous subsequent oxygen availability and organic carbon burial in the eastern subtropical atlantic however without turning the ocean anoxic the match between modelling results and stratigraphic isotopic data support previous studies summarized in jenkyns h c 2003 evidence for rapid climate change in the mesozoic palaeogene greenhouse world the royal society 361 1885 1916 in that methane emission from marine hydrates albeit moderate in dimension may have been the trigger for oae 1b though we can not finally rule out alternative mechanisms following the hydrate mechanism a total of 1 15 1018 g methane carbon 13c 60 equivalent to about 10 to the total modern gas hydrate inventory generated the 13ccarb profile recorded in the section modelling suggests a combination of moderate scale methane pulses supplemented by continuous methane emission at elevated levels over not vert similar 25 000 yr the proposed mechanism though difficult to finally confirm in the geological past is arguably more likely to occur in a warmer world and apparently perturbs global climate and ocean chemistry almost instantaneously this study shows that once set off this mechanism can maintain earth s climate in a perturbed mode over geological time leading to pronounced changes in regional climate

nearshore euxinia in the photic zone of an ancient sea abstract evidence for photic zone euxinia pze in ancient oceans is widespread and commonly associated with global climate change and biotic events however evidence of pze in marginal settings is commonly extrapolated to infer basin scale characteristics to explore the relationship between euxinia in marginal settings and the wider basin in one palaeozoic context we have conducted a detailed spatial and temporal examination the palaeowater column redox state from the polish sector of the southern permian basin spb during deposition of the zechstein lopingian second carbonate main dolomite cycle sediments from toe of slope slope and hypersaline lagoonal settings of the northeastern margin of the spb contain abundant chlorobactane isorenieratane and their likely degradation products c 15 to c 31 2 3 6 aryl isoprenoids these indicate that part of the photic zone was euxinic during significant intervals of the main dolomite deposition further evidence for strongly anoxic conditions includes the occurrence of c 28 bisnorhopane high concentrations of pentakishomohopanes i e high homohopane indices and the occurrence of framboidal and native sulphur crystals in slope facies however a lack of these signatures in basinal settings indicates that strongly reducing conditions were restricted to the slope and toe of slope locations even in these settings however highly variable homohopane indices and concentrations of isorenieratene and chlorobactene derivatives as well as the presence of benthic fauna and bioturbation indicate that anoxia fluctuated throughout deposition of the main dolomite likely on a variety of timescales sterane distributions are also variable suggesting a dynamic ecosystem likely exhibiting a strong response to environmental forcing overall it appears that high but episodic primary bioproductivity of organic matter was concentrated on the northeastern slope and restricted lagoons leading to the formation of source rocks for petroleum however the temporal and geographical restriction of anoxia appears to have prevented the accumulation of large or more widespread quantities of organic matter and in fact toc contents exhibit poor correlation with ecological and anoxia indicators this model indicates that strong evidence for pze in shelf and slope facies need not be associated with widespread basin scale anoxia with implications for organic matter burial carbon cycling and biotic crises

p wave tomography and origin of the changbai intraplate volcano in northeast asia abstract we present the first seismic image of the upper mantle beneath the active intraplate changbai volcano in northeast asia determined by teleseismic travel time tomography the data are measured at a new seismic network consisting of 19 portable stations and 3 permanent stations our results show a columnar low velocity anomaly extending to 400 km depth with a p wave velocity reduction of up to 3 high velocity anomalies are visible in the mantle transition zone and deep focus earthquakes occur at depths of 500 600 km under the region suggesting that the subducting pacific slab is stagnant in the transition zone as imaged clearly by global tomography these results suggest that the intraplate changbai volcano is not a hotspot like hawaii but a kind of back arc volcano related to the deep subduction and stagnancy of the pacific slab under northeast asia

redox controlled preservation of organic matter during oae 3 within the western interior seaway during the cretaceous widespread black shale deposition occurred during a series of oceanic anoxic events oaes multiple processes are known to control the deposition of marine black shales including changes in primary productivity organic matter preservation and dilution oaes offer an opportunity to evaluate the relative roles of these forcing factors the youngest of these events the coniacian to santonian oae 3 resulted in a prolonged organic carbon burial event in shallow and restricted marine environments including the western interior seaway new high resolution isotope organic and trace metal records from the latest turonian to early santonian niobrara formation are used to characterize the amount and composition of organic matter preserved as well as the geochemical conditions under which it accumulated redox sensitive metals mo mn and re indicate a gradual drawdown of oxygen leading into the abrupt onset of organic carbon rich up to 8 deposition high hydrogen indices hi and organic carbon to total nitrogen ratios c n demonstrate that the elemental composition of preserved marine organic matter is distinct under different redox conditions local changes in 13c indicate that redox controlled early diagenesis can also significantly alter 13corg records these results demonstrate that the development of anoxia is of primary importance in triggering the prolonged carbon burial in the niobrara formation sea level reconstructions 18o results and mo total organic carbon ratios suggest that stratification and enhanced bottom water restriction caused the drawdown of bottom water oxygen increased nutrients from benthic regeneration and or continental runoff may have sustained primary productivity

surface wave tomography of eastern and central tibet from two plane wave inversion rayleigh wave and love wave phase velocity mapssurface wave tomography of eastern and central tibet from two plane wave inversion rayleigh wave and love wave phase velocity maps