response of nannoplankton to early eocene ocean destratification abstract nannoplankton play a significant role in the global carbon cycle changes in the composition of the assemblage can influence primary productivity carbon burial and ultimately climate here counts of nannofossils in eocene samples document one of the largest nannoplankton assemblage turnovers of the cenozoic era this event is marked by the global expansion of reticulofenestra at the termination of the early eocene climatic optimum eeco and continues through the progressive cooling to the earliest oligocene glaciation to understand the mechanisms driving this assemblage shift we use multivariate statistical techniques and carbon and oxygen isotope records from localities worldwide we find that the turnover in the global nannofossil assemblage is tied to thermal destratification of the ocean and a coincident decrease in the efficiency of the oceanic biologic pump at the height of the eeco we propose that increased vertical mixing and increased nutrient supply to surface waters during the eeco caused a shift in the trophic structure towards enhanced productivity influencing the global nannoplankton population

tropical sea surface temperature reconstruction for the early paleogene using mg ca ratios of planktonic foraminifera 1 to understand the climate dynamics of hypothesized past greenhouse intervals it is essential to constrain tropical sea surface temperatures sst yet existing proxy records give conflicting results here we present the first mg ca based study of pre quaternary sst and investigate early paleogene late paleocene through late middle eocene 58 6 39 8 ma tropical temperatures using planktonic foraminifera belonging to the genus morozovella from ocean drilling program site 865 on allison guyot western central equatorial pacific ocean calcification temperatures similar to or warmer than modern tropical sst are calculated using a range of assumptions regarding diagenesis temperature calibration and seawater mg ca long term warming is observed into the early eocene 54 8 49 0 ma with peak sst between 51 and 48 ma and rapid cooling of 4 c beginning at 48 ma these findings are inconsistent with the 18o based sst previously estimated for this site

triassic bedded cherts in central japan are not pelagic although the origin of bedded radiolarian cherts in orogenic belts has been widely debated1 15 their geochemistry is still poorly understood triassic bedded radiolarian cherts occur extensively in the japanese islands and are generally not associated with ophiolitic rocks but rather with clastic rocks we present here chemical data on the triassic bedded cherts of kamiaso in central japan the relationship of sio2 with al2o3 tio2 and zr shows that the bedded cherts have been formed by a simple mixing of biogenic silica derived from radiolarians and sponge spicules with lithogenic materials the ratios of several elements relative to tio2 strongly suggest that the shale partings and lithogenic portions of the cherts are consanguineous sedimentary structures as well as the geochemical evidence suggest that most kamiaso cherts are turbidity current deposits our geochemical and geological data compared with those of recent marine sediments from various environments demonstrate that the triassic cherts and associated shale partings are not deep pelagic in origin but formed in an offshore or marginal sea environment

aquaplanet experiments using cam s variable resolution dynamical core abstracta variable resolution option has been added within the spectral element se dynamical core of the u s department of energy doe ncar community atmosphere model cam cam se allows for static refinement via conforming quadrilateral meshes on the cubed sphere this paper investigates the effect of mesh refinement in a climate model by running variable resolution var res simulations on an aquaplanet the variable resolution grid is a 2 222 km grid with a refined patch of 0 25 28 km resolution centered at the equator climatology statistics from these simulations are compared to globally uniform runs of 2 and 0 25 a significant resolution dependence exists when using the cam version 4 cam4 subgrid physical parameterization package across scales global cloud fraction decreases and equatorial precipitation increases with finer horizontal resolution resulting in drastically different climates between the uniform grid runs and a physics induced grid imprinting in the var res simulation

ocean circulation and calcareous nannoplankton evolution during the jurassic and cretaceous abstract spatial and temporal distribution of calcareous nannoplankton aid in the reconstruction of ocean circulation during the cretaceous biogeographic patterns of calcareous nannoplankton during the late cretaceous are mostly zonal reflecting mostly latitudinal gradients of surface water temperature during the middle cretaceous calcareous nannofossil assemblages are more strongly affected by surface water fertility concentration of limiting nutrients especially in a wide tropical belt between 50 and 45 n latitudes major upwelling regions off northwest africa in the south atlantic and the equatorial pacific divergence are apparent temporal changes in the composition of middle cretaceous nannofloras are indicative of changes in surface water fertility and vertical mixing at frequencies of tens to hundreds of kiloyears ka changes in the intensity of atmospheric circulation with frequencies close to the milankovitch cycles appear to be the ultimate cause of these minor changes in the circulation of the upper ocean calcareous nannofossil preservation patterns show that during the middle cretaceous deep waters were quite homogeneous with respect to carbonate saturation in the atlantic ocean but not in the indo pacific ocean where a more distinctive calcite compensation depth ccd is apparent water mass structure of the major oceans during the mesozoic was thus quite different taxonomic evolution of calcareous nannofossils was also strongly affected by ocean circulation and fertility major peaks in the rates of diversification coincide with anoxic events that is periods of increased preservation of organic carbon in the oceans which coincide with high sea level stands during anoxic events ocean circulation was sluggish vertical mixing was slow deep ocean ventilation poor and the concentration of limiting nutrients in surface waters was low increased competition for limiting nutrients and possibly preferential cropping of the dominant forms by zooplankton resulted in increased rates oof speciation during anoxic events periods of major production of nannofossil carbonate coincided with low sea level stands when oceans were more vigorously stirred and surface waters were more fertile the first such period was the latest jurassic when calcareous nannoplankton invaded the open oceans and became the major carbonate producers in the pelagic realm during the mesozoic the frequency of peaks and troughs in evolutionary rates is on the order of 10 30 ma and appears to be irregular the coincidence of periods of anoxia with high sea level stands which in turn appear to be caused by more rapid sea floor spreading indicates that the ultimate diving forces of nannoplankton evolution are processes in the earth s mantle these major tectonically driven fluctuations in ocean atmosphere circulation with frequencies of a few million to a few tens of millions of years are hereby named fischer cycles superimposed astronomically driven milankovitch cycles affected relative abundance patterns but not taxonomic evolution of calcareous nannoplankton rates of nannoplankton extinction are about five times higher than background rates at the end of the jurassic and orders of magnitude higher in the latest cretaceous possibly indicating a terrestrial or extraterrestrial catastrophe

selective calcareous nannoplankton survivorship at the cretaceous tertiary boundary calcareous nannoplankton underwent devastating diversity loss at the cretaceous tertiary boundary 65 5 ma but recovered rapidly in the early paleocene from a small number of survivor species an understanding of this survivorship has been hampered by uncertainties introduced by reworking and mixing but new high resolution assemblage data from the northwest pacific shatsky rise ocean drilling program site 1210 allow the unequivocal identification of 10 survivors evidence of shared adaptive strategies among these species provides the first indication that the extinctions were selective with survival limited to a few neritic and or opportunistic species probably facilitated by hardiness and or life cycle escape strategies 2005 geological society of america

middle eocene lower oligocene calcareous nannofossil biostratigraphy and paleoceanographic implications from site 711 equatorial indian ocean abstract nannofossil data from odp site 711 equatorial indian ocean yield a set of consistent reliable biohorizons that form the basis of a revised calcareous nannofossil biostratigraphy for the low latitude eocene oligocene we discuss 31 biohorizons occurring over an 11 myr time interval which we correlate to previous magnetostratigraphic data calcareous nannofossils from the middle eocene through the lower oligocene of the studied section are characterized by moderately well preserved assemblages consisting largely of low latitude and cosmopolitan species a significant nannofossil dissolution interval is evidenced at the middle eocene climatic optimum meco we document a significant increase in late eocene nannoplankton exhibiting a eutrophic preference analysis of the assemblage suggests important changes in the equatorial oceanic regime just before the onset of the eocene oligocene transition eot that foreshadow the more dramatic climatic shift of the early oligocene

nannoplankton origination events and environmental changes in the late paleocene and early eocene the origination of six nannoplankton species in the late paleocene to middle eocene involves significant change in the entire nannofossil assemblage the change began at the first occurrence and accelerates at the increase in abundance of the new species the changes in the environment generally reflect the preferred ecology of the originating species the species that originated in the late paleocene to early eocene outside of the paleocene eocene thermal maximum petm are generally thought to be oligotrophic taxa adapted to warm water conditions during this long interval temperatures were generally increasing and nutrient availability was decreasing conditions that would have been advantageous for the originating taxa conversely the species that originated in the middle eocene are generally thought to be mesotrophs adapted to colder water conditions these taxa were selected for during a time of generally increasing nutrient availability and decreasing temperature orbital stratigraphy indicates that the first occurrences of three paleocene taxa are time transgressive by up to 400 kyr the only event that appears to be synchronous is the abundance increase of zygrhablithus bijugatus during the petm this species is thought to be mesotrophic and replaces the genus fasciculithus at a time when nutrient availability was likely increasing rapidly

response of calcareous nannofossils to the paleocene eocene thermal maximum from a shelf section in jordan abstract the paleocene eocene thermal maximum petm is known as an approximately 200 kyr long lasting interval of extreme global warming accompanied by major alterations in the ocean atmosphere system these include a negative carbon isotope excursion intense carbonate dissolution and biotic changes of marine floras and faunas the current study reports the response of calcareous nannofossils across the paleocene eocene boundary in a paleoshelf setting in jordan core os 28 clearly marked by a negative 13 c org excursion and the occurrence of characteristic excursion taxa e g discoaster araneus rhomboaster spp coccolithus bownii while this section suffers from intense dissolution at the onset of the event and the peak of the isotopic excursion it retains well preserved diverse nannofossil assemblages from the pre petm petm recovery and post petm intervals these assemblages are dominated by two taxa of inferred mesotrophic affinities coccolithus pelagicus toweius spp and show only low abundances of oligotrophic taxa discoaster spp fasciculithus spp sphenolithus spp overall there appear to be only relatively low level changes in the general assemblage composition across the petm during the post petm however there was a gradual decrease in relative abundance of c pelagicus and toweius spp this decline co coccured with a relative increase of coccolithus bownii and coccolithus foraminis and in its later phase was accompanied by an increase in the relative abundance of sphenolithus spp these changes indicate a possible shift towards less fertile conditions following the hyperthermal event the relatively muted signal of biotic change associated with the petm interval at this site was partly a consequence of poor preservation within the key sequence of the studied core on the other hand the low signal may also be indicative for local environment processes such as variations in riverine sourced nutrients salinity turbidity operating on a regional scale these local factors overrode the direct and indirect temperature signals that are the dominant control on nannofossil communities across the petm in open ocean sites finally the assemblages from the jordan section highlight further the overall spatial heterogeneity in reported responses of shelf area communities to the petm interval these heterogeneities have been observed in shelf assemblages from tanzania new jersey and the tethyan margins which again points to the strong influence of regional controls like river input in more marginal settings

a balanced tropical cyclone test case for agcms with background vertical wind shear abstractthis paper presents a balanced tropical cyclone tc test case designed to improve current understanding of how atmospheric general circulation model agcm configurations affect simulated tc development and behavior it consists of an analytic initial condition comprising two independently balanced components the first provides a vortical tc seed while the second adds a planetary scale zonal flow with height dependent velocity and imposes background vertical wind shear vws on the tc seed the environmental flow satisfies the steady state hydrostatic primitive equations in spherical coordinates and is in balance with other background field variables e g temperature surface geopotential the evolution of idealized tcs in the test case framework is illustrated in 10 day simulations performed with the community atmosphere model version 5 1 1 cam 5 1 1 environmental wind profiles with different magnitudes directions and vertical inflection points are applied to ensure that the technique

tectonic control of guadalupian lopingian cherts in northwestern sichuan basin south china abstact cherts have been considered to be formed mainly through processes involving biosilicification riverine inputs and hydrothermal activities in the permian massive cherts are widely distributed in south china bearing significant implications for the reconstruction of paleogeography and paleoceanography of the eastern paleo tethys ocean the origin of the permian cherts in south china however remains inconclusive due to a lack of systematic petrographic and geochemical study in this article we analyze the petrologic and geochemical characteristics of the cherts collected from five outcrops in the northwestern sichuan basin south china these cherts are found from the upper guadalupian maokou formation ca 268 259 ma and upper lopingian dalong formation ca 254 252 ma field and microscopic observations suggest that cherts from the maokou formation occur mainly in nodular forms and consist of microcrystalline quartz silicified bioclasts and siliceous fossil debris both petrographic observation and geochemical analysis suggest that the maokou cherts are mainly of hydrothermal origin near deep faults in the southwest and of biogenetic origin with less hydrothermal influence in the northeast of the studied area the dalong cherts occur in both nodular and bedded forms with more abundant siliceous fossil debris than the maokou cherts major trace and rare earth element data support that the dalong cherts are influenced by both biosilicification and hydrothermal activities the spatial heterogeneity of the cherts origin in south china is largely controlled by tectonic activities associated with the emeishan large igneous province elip event and the closure of the paleo tethys ocean the troughs formed by the extensional tectonic activity linked to the elip could provide accommodation space and activate deep faults allowing the rise of silicon rich hydrothermal fluids from the deep and nutrient rich water from volcanogenic upwellings subsequent cooling may have facilitated the precipitation of large amounts of silica and the formation of cherts in the study region this work demonstrates that the origin of the guadalupian lopingian cherts in south china is predominantly controlled by tectonic and biological activities which sheds light on the global permian chert event

geochemistry of the mesozoic bedded cherts of central baja california vizcaino cedros san benito implications for paleogeographic reconstruction of an old oceanic basin abstract in central baja california vizcaino peninsula and cedros and san benito islands two distinct radiolarian bedded chert sequences of late triassic and late jurassic lowermost cretaceous age can be differentiated on lithostratigraphic and geochemical criteria these bedded chert sequences are part of the conformable sedimentary cover of more or less dismembered ophiolites which are overthrusted by the san andres cedros volcanic arc system of middle late jurassic age major and trace elements permit paleogeographic zonation of the late jurassic lowermost cretaceous radiolarites lying conformably upon ophiolites considered as fragments of an oceanic basin floor which developed westward of the san andres volcanic arc progressive accretion of this oceanic basin floor along the continental margin is supported by the fact that the more distal radiolarian chert sequences belong to the lowermost structural units of this area

an analytic vortex initialization technique for idealized tropical cyclone studies in agcms abstract the paper discusses the design of idealized tropical cyclone experiments in atmospheric general circulation models agcms the evolution of an initially weak warm core vortex is investigated over a 10 day period with varying initial conditions that include variations of the maximum wind speed and radius of maximum wind the initialization of the vortex is built upon prescribed 3d moisture pressure temperature and velocity fields that are embedded into tropical environmental conditions the initial fields are in exact hydrostatic and gradient wind balance in an axisymmetric form the formulation is then generalized to provide analytic initial conditions for an approximately balanced vortex in agcms with height based vertical coordinates an extension for global models with pressure based vertical coordinates is presented the analytic initialization technique can easily be implemented on any agcm computational grid the characteristics of the idealized tropical cyclone experiments are illustr

geochemical constraints on the depositional setting of palaeozoic cherts from the new england orogen nsw eastern australia despite widespread occurrences of radiolarian cherts within the new england orogen neo their age geochemistry and sedimentology have not been studied recent radiolarian age determinations of these cherts have markedly changed previous conceptions as to their age geochemical analyses constrain the depositional setting of two distinctive types of chert facies within two terranes of the orogen type i are ribbon bedded cherts of the djungati terrane and varicoloured ribbon bedded cherts of the anaiwan terrane low values of al al fe mn and corresponding high values of fe2o3 indicate a possible hydrothermal contribution while mnotio2 ratios indicate accumulation far from terrigenous sedimentary influences high si si al fe ratios indicate a high biogenic content type ii are tuffaceous cherts which are common in both terranes high values of al al fe mn and low si si al fe and mnotio2 values indicate deposition in an environment which is more proximal to a terrigenous source than that of type i cherts the abundance of both na2o and al2o3 increases relative to silica in type ii cherts and indicates dilution by the input of volcanic ash this is further substantiated by the ternary k ba v 10 plot an al 1bfe 1bmn diagram indicates that type ii cherts are non hydrothermal in origin both chert types were conveyed into a trench by subduction processes as subduction continued hemipelagic sedimentation was swamped by the influx of coarse grained volcaniclastic sediments deposited from turbidity currents reaching the trench the diverse sedimentary types were tectonically intercalated to form sequences of imbricate thrust slices within two distinctly different subduction complexes which have subsequently been tectonically juxtaposed

middle eocene to late oligocene antarctic glaciation deglaciation and southern ocean productivity during the eocene oligocene transition earth cooled significantly from a greenhouse to an icehouse climate nannofossil assemblages from southern ocean sites enable evaluation of paleoceanographic changes and hence of the oceanic response to antarctic ice sheet evolution during the eocene and oligocene a combination of environmental factors such as sea surface temperature and nutrient availability is recorded by the nannofossil assemblages of and can be interpreted as responses to the following changes a cooling trend started in the middle eocene was interrupted by warming during the middle eocene climatic optimum and by short cooling episodes the cooling episode at 39 6 ma preceded a shift toward an interval that was dominated by oligotrophic nannofossil assemblages from 39 1 to 36 2 ma we suggest that oligotrophic conditions were associated with increased water mass stratification low nutrient contents and high efficiency of the oceanic biological pump that in turn promoted sequestration of carbon from surface waters which favored cooling after 36 2 ma we document a large synchronous surface water productivity turnover with a dominant eutrophic nannofossil assemblage that was accompanied by a pronounced increase in magnetotactic bacterial abundance this turnover reflects a response of coccolithophorids to changed nutrient inputs that was likely related to partial deglaciation of a transient antarctic ice sheet and or to iron delivery to the sea surface eutrophic conditions were maintained throughout the oligocene which was characterized by a nannofossil assemblage shift toward cool conditions at the eocene oligocene transition finally a warm nannofossil assemblage in the late oligocene indicates a warming phase

late paleozoic radiolarian ages from the gwydir terrane new england orogen eastern australia discoveries of late devonian early mississippian radiolaria in the gwydir terrane eastern australia indicate that much of the terrane is younger than previously thought radiolaria provide valuable constraints on the timing of the development of the gwydir terrane moreover this new biostratigraphic data indicate that previously published models detailing the development of the new england orogen need to be reappraised

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

manganiferous cherts of the franciscan assemblage i general geology ancient and modern analogues and implications for hydrothermal convection at oceanic spreading centers there are several hundred ophiolitic manganiferous chert deposits primarily of late jurassic to early cretaceous age known within the franciscan assemblage of california the sequences typically consist of one to three massive manganiferous chert lenses containing 30 to 50 percent mn and averaging 1 m in thickness by 15 m subcircular diameter these are separated by an average 2 to 10 m of thin bedded radiolarian cherts and overlie basalts or greenstones both their geology and chemistry indicate that the ore lenses are hydrothermal and may have formed on the flanks of a mid ocean ridge or within a back arc basin it is proposed that the sequences developed as a result of sea floor spreading over a series of deep hydrothermal seawater convection cells paralleling a spreading center and spaced roughly 5 to 10 km apart chemical profiles of mn fe si al cu ni zn co ba ti the rare earth elements and 87 sr 86 sr have been determined through two complete sections these profiles indicate hydrothermal input of mn si cu ni zn and ba and detrital or hydrogenous input of al and co they illustrate the use of ti as a measure of relative detrital sedimentation rates fe is strongly fractionated from mn within the ores fe mn 0 1 and fe mn ratios decrease upward throughout each section suggesting preferential deposition of fe within the sediment and of mn at the seawater interface rare earth element distributions reflect the interaction of sea water and underlying basalts sr isotopic ratios of the ores and basalts demonstrate both strong and moderate seawater influences respectively fluid inclusion analyses on veins of undetermined age show seawater salinity temperatures of roughly 200 degrees c and tentative entrapment pressures corresponding to 1 700 m water depth early and intermediate veins were injected into unconsolidated siliceous sediment producing a characteristic bleached and pseudobrecciated texture an analogy is drawn with the present day field of hydrothermal mounds near the galapagos rift and with ophiolitic complexes of the northern apennines and other localities

geochemical characteristics and depositional environments of cherts and associated rocks in the franciscan and shimanto terranes abstract analyses of 122 jurassic cretaceous rock samples from the franciscan terrane california and 24 cretaceous samples from the shimanto terrane southwest japan show that the cherts and associated rocks accompanied by pillow basalts are enriched in fe and mn which may have been derived from hydrothermal activities the results of the fraction analyses for terrigenous basaltic hydrothermal and biogenic end members in the franciscan rocks show that hydrothermal emanations caused iron and manganese enrichment in the rock samples and played an important role in the formation of siliceous rocks vertical variations of the hydrothermal fraction and tio2 normalized values for hydrothermal elements such as fe mn ni zn y and pb show a possibility that the bedded cherts of the franciscan terrane were deposited in a hydrothermal field on or near some active oceanic ridge for more than 30 ma and were a remnant slice of oceanic crust added to the north american continent on the other hand from the field occurrences and vertical variations of tio2 normalized values of hydrothermal elements the shimanto rocks are inferred to have been deposited in a hemipelagic environment such as marginal and inter arc basins

sensitivity of equatorial convection to horizontal resolution in aquaplanet simulations with a variable resolution gcm abstract climate simulations using idealized zonally symmetric boundary conditions an aquaplanet are performed in order to highlight possible deviations from zonality introduced by the spatial variations in resolution caused by the variable resolution technique simulations at three different uniform resolutions with spectral truncations t21 t63 and t106 are used as control simulations and analyzed in order to describe the zonal climate simulated by this version of the arpege climat general circulation model and establish its sensitivity to varying spatial resolution the model simulates a single equatorial precipitation maximum in which the activity of the convective cells is modulated by westward and eastward propagating equatorial waves depending on the resolution a simulation with the variable resolution technique using a truncation t63 and a stretching factor of 3 with the maximum resolution pole placed at the equator is then compared to the uniform resolution simulations deviations from the

fluctuations in the trophic resource continuum a factor in global diversity cycles the trophic resource continuum trc in euphotic zones of the world s oceans is the spectrum of conditions from the richest runoff and upwelling areas to the most nutrient deficient subtropical seas that spectral range has likely varied through geologic history as more efficient phytoplankton taxa evolved as oceanic circulation rates changed and in response to oceanic mixing events reduced rates of oceanic turnover should produce regionally intensified eutrophy and oligotrophy that is trc expansion because oceanic waters as a whole are relatively nutrient rich increased rates of oceanic turnover should prevent extremely eutrophic and extremely oligotrophic conditions from developing causing trc contraction global biotic diversities in the oceans are strongly influenced by communities in oligotrophic environments nutrient deficient waters are more stable and more transparent than richer waters permitting higher degrees of specialization sparse nutrient supplies necessitate smaller phytoplankton and longer more complex food chains preservation potential of oligotrophic biotas is also greater because calcareous taxa are more prevalent and because calcium carbonate is less apt to be bioeroded or dissolved fluctuations in the trc should profoundly affect diversity of habitats within the euphotic zone of the oceans the evolutionary response to a trc expansion diversification would occur in a geologic time frame of millions of years while evolutionary responses to a trc contraction including extinction could occur in a biological time frame of generations a simple model indicates that a reduction in the trophic resource continuum from expansion during a major marine transgression down to modern levels could result in loss of 40 of the euphotic habitats how fluctuations in the trc control diversity of euphotic habitats in the oceans provides an hypothesis by which to interpret global taxonomic diversity cycles as well as taxonomically selective extinctions changes in species dominance and some morphologic trends

astronomical calibration of the paleocene time the first complete cyclic sedimentary successions for the early paleogene from drilling multiple holes have been retrieved during two odp expeditions leg 198 shatsky rise nw pacific ocean and leg 208 walvis ridge se atlantic ocean these new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the atlantic and the pacific oceans covering the entire paleocene epoch based on the identification of the stable long eccentricity cycle 405 kyr high resolution x ray fluorescence xrf core scanner and non destructive core logging data from sites 1209 through 1211 leg 198 and sites 1262 1267 leg 208 are the basis for such a robust chronostratigraphy former investigated marine odp sites 1001 and 1051 and land based e g zumaia sections have been integrated as well the high fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into greenhouse climate variability in the early paleogene we demonstrate that the paleocene epoch covers 24 long eccentricity cycles we also show that no definite absolute age datums for the k pg boundary or the paleocene eocene thermal maximum petm can be provided by now because of still existing uncertainties in orbital solutions and radiometric dating however we provide two options for tuning of the paleocene which are only offset by 405 kyr our orbitally calibrated integrated leg 208 magnetostratigraphy is used to revise the geomagnetic polarity time scale gpts for chron c29 to c25 we established a high resolution calcareous nannofossil biostratigraphy for the south atlantic which allows a much more detailed relative scaling of stages with biozones the re evaluation of the south atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron c28r c27n and c26n

ocean acidification and surface water carbonate production across the paleocene eocene thermal maximum the addition of massive amounts of carbon to the ocean atmosphere system at the paleocene eocene thermal maximum petm similar to 55 ma caused deep ocean acidification evidenced by widespread dissolution of sea floor carbonate sediments because of the strong effect of this dissolution on the preserved record of calcium carbonate it has been difficult to evaluate whether changes in surface water chemistry affected carbonate production at the same time here we investigate the production of biogenic carbonate in surface waters by testing a method which combines fossil calcareous nannoplankton counts with taxon specific sr ca data an indicator of coccolithophore production reconstructed nannoplankton production at ocean drilling program odp sites 690 southern ocean 1209 pacific ocean and bass river new jersey did not appear to vary significantly across the petm indicating that on geological timescales there is no evidence for interruption of phytoplankton carbonate production despite the major assemblage shifts associated with this interval either levels of carbonate chemistry change in surface waters were relatively low perhaps a function of co2 emission rates or calcareous nannoplankton were relatively insensitive to these changes compared with their response to other environmental parameters namely temperature and nutrient availability c 2010 elsevier bm all rights reserved

petrogenesis of graphitic cherts in the armorican segment of the cadomian orogenic belt nw france graphitic cherts are interbedded within terrigenous sediments in the cadomian orogenic belt of end proterozoic age in the armorican massif nw france the graphitic cherts are of two types massive cherts essentially composed of quartz sio2 96 and with rare sedimentary structures laminated cherts containing up to 3ae4 al2o3 and 92 98 sio2 sedimentary structures observed in the laminated cherts are indicative of a restricted hypersaline tidal or supratidal environment the origins of both types of chert are to be found in the diagenetic processes of silification of terrigenous and mixed terrigenousevaporitic facies these processes which could be mediated by the presence of organic matter were controlled by the migration of the freshwater saltwater mixing zone during periods of relative sea level change the proposed diagenetic origin for the cherts places a number of constraints on their use in the establishment of stratigraphic correlations

calcareous nannoplankton response to late albian oceanic anoxic event 1d in the western north atlantic well preserved nannofossil and stable isotope records from the mid cretaceous of ocean drilling project leg 171b western north atlantic indicate cyclical productivity based variations in surface water characteristics suggesting orbitally paced changes in upwelling intensity and the strength of deep mixing associated with oceanic anoxic event oae 1d paleontologic and isotopic evidence suggest that collapse of upper water column stratification associated with oae1d was preceded by approximately 1 m y of progressively decreasing water column stability and increasing surface water fertility thirteen species went extinct during a short ca 200 k y interval associated with oae1d nine of these have morphological characters suggesting adaptation to specific depths in the photic zone simultaneous extinction of these depth zoned species suggests that stratification collapse disrupted the habitat space for these specialized forms resulting in extinction a cyclostratigraphic model provides age estimates of several important nannofossil datums including the first appearances of eiffellithus turriseiffelii 100 95 ma and corollithion kennedyi 99 55 ma

warming the fuel for the fire evidence for the thermal dissociation of methane hydrate during the paleocene eocene thermal maximum dramatic warming and upheaval of the carbon system at the end of the paleocene epoch have been linked to massive dissociation of sedimentary methane hydrate however testing the paleocene eocene thermal maximum hydrate dissociation hypothesis has been hindered by the inability of available proxy records to resolve the initial sequence of events the cause of the paleocene eocene thermal maximum carbon isotope excursion remains speculative primarily due to uncertainties in the timing and duration of the paleocene eocene thermal maximum we present new high resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from ocean drilling program site 690 weddell sea southern ocean demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface water warming both of these findings support the thermal dissociation of methane hydrate as the cause of the paleocene eocene thermal maximum carbon isotope excursion furthermore the data reveal that the methane derived carbon was mixed from the surface ocean downward suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation

on the duration of magnetochrons c24r and c25n and the timing of early eocene global warming events implications from the ocean drilling program leg 208 walvis ridge depth transect 1 five sections drilled in multiple holes over a depth transect of more than 2200 m at the walvis ridge se atlantic during ocean drilling program odp leg 208 resulted in the first complete early paleogene deep sea record here we present high resolution stratigraphic records spanning a 4 3 million yearlong interval of the late paleocene to early eocene this interval includes the paleocene eocene thermal maximum petm as well as the eocene thermal maximum etm 2 event a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records and shipboard color data these records were used to refine the shipboard derived spliced composite depth for each site and with a record from odp site 1051 were then used to establish a continuous time series over this interval extensive spectral analysis reveals that the early paleogene sedimentary cyclicity is dominated by precession modulated by the short 100 kyr and long 405 kyr eccentricity cycles counting of precession related cycles at multiple sites results in revised estimates for the duration of magnetochrons c24r and c25n direct comparison between the amplitude modulation of the precession component derived from xrf data and recent models of earth s orbital eccentricity suggests that the onset of the petm and etm2 are related to a 100 kyr eccentricity maximum both events are approximately a quarter of a period offset from a maximum in the 405 kyr eccentricity cycle with the major difference that the petm is lagging and etm2 is leading a 405 kyr eccentricity maximum absolute age estimates for the petm etm2 and the magnetochron boundaries that are consistent with recalibrated radiometric ages and recent models of earth s orbital eccentricity cannot be precisely determined at present because of too large uncertainties in these methods nevertheless we provide two possible tuning options which demonstrate the potential for the development of a cyclostratigraphic framework based on the stable 405 kyr eccentricity cycle for the entire paleogene

using variable resolution meshes to model tropical cyclones in the community atmosphere model abstracta statically nested variable mesh option has recently been introduced into the community atmosphere model s cam s spectral element se dynamical core that has become the default in cam version 5 3 this paper presents a series of tests of increasing complexity that highlight the use of variable resolution grids in cam se to improve tropical cyclone representation by dynamically resolving storms without requiring the computational demand of a global high resolution grid as a simplified initial test a dry vortex is advected through grid transition regions in variable resolution meshes on an irrotational planet with the cam subgrid parameterization package turned off vortex structure and intensity is only affected by grid resolution and no spurious artifacts are observed cam se model simulations using an idealized tropical cyclone test case on an aquaplanet show no numerical distortion or wave reflection when the cyclone interacts with an abrupt transition region using the same test case th

late paleocene to eocene paleoceanography of the equatorial pacific ocean stable isotopes recorded at ocean drilling program site 865 allison guyot an expanded and largely complete upper paleocene to upper eocene section was recovered from the pelagic cap overlying allison guyot mid pacific mountains at ocean drilling program odp site 865 18o26 n 179o33 w paleodepth 1300 1500 m reconstructions show that the site was within a few degrees of the equator during the paleogene because no other paleogene sections have been recovered in the pacific ocean at such a low latitude site 865 provides a unique record of equatorial pacific paleoceanography detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa species of acarinina morozovella and subbotina we studied benthic foraminiferal isotopes at much lower resolution on species of cibicidoides and lenticulina nuttallides truernpyi and gavelinella beccariiformis because of their exceptional rarity the 5180 and 513c stratigraphies from site 865 are generally similar to those derived from other paleocene and eocene sections the planktonic foraminiferal records at site 865 however include significantly less short term single sample variability than those from higher latitude sites indicating that this tropical oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability low amplitude 0 1 0 8 o oscillations on timescales of 250 000 to 300 000 years correlate between the 513c records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters peak sea surface temperatures of 24o 25oc occurred in the earliest eocene followed by a rapid cooling of 3 6oc in the late early eocene temperatures remained cool and stable through the middle eocene in the late eocene surface water temperatures decreased further vertical temperature gradients decreased dramatically in the late paleocene and were relatively constant through much of the eocene but increased markedly in the late eocene intermediate waters warmed through the late paleocene reaching a maximum temperature of 10oc in the early eocene cooling in the middle and late eocene paralleled that of surface waters with latest eocene temperatures below 5oc extinction patterns of benthic foraminifera in the latest paleocene were similar to those observed at other pacific sites and were coeval with a short term very rapid negative excursion in 513c values in planktonic and benthic taxa as at other sites during this excursion benthic foraminiferal 5180 values decreased markedly indicating warming of 4 to 6oc for tropical intermediate waters while planktonic taxa show slight warming 1 oc followed by 2oc of cooling convergence of 5180 values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion these data are consistent with the hypothesis that equatorial pacific surface waters were a potential source of warm higher salinity waters which filled portions of the deep ocean in the latest paleocene oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4oc at the peak of the excursion suggesting some fundamental change in global heat transport

evaluation of the astronomical time scale for the paleocene and earliest eocene abstract the astronomical tuned time scale is rapidly extended into the paleogene but due to the existence of an eocene gap different tuning options had to be presented for the paleocene these options differ both in number and tuning of 405 kyr eccentricity related cycles and are only partially consistent with recalculated 40 ar 39 ar constraints for the cretaceous paleogene k pg and paleocene eocene p e boundaries in this paper we evaluate the cyclostratigraphic interpretation of records from odp leg 198 and 208 sites and the zumaia section to solve the problem of the different tuning options we found that the interval between the k pg boundary and the early late paleocene biotic event elpe comprises 17 instead of 16 405 kyr eccentricity related cycles as previously proposed while the entire paleocene contains 25 405 kyr cycles starting from 40 ar 39 ar age constraints for the k pg boundary a new tuning to 405 kyr eccentricity is presented for the paleocene and earliest eocene which results in ages of 66 0 and 56 0 ma for the k pg and p e boundaries respectively this tuning introduces considerable differences in age for a number of nannofossil events at odp sites 1209 and 1262 in the interval between 61 and 63 ma but eliminates large and abrupt changes in the seafloor spreading rate the tuning seems further consistent with recalculated 40 ar 39 ar ages for ash layer 17 of early eocene age however despite this apparent consistency with existing radio isotopic constraints an alternative 405 kyr younger or less likely older tuning cannot be excluded at this stage

changes in calcareous nannofossil assemblages across the paleocene eocene transition from the paleo equatorial pacific ocean quantitative analyses of selected calcareous nannofossils in deep sea sections recovered from the paleo equatorial pacific odp leg 199 provide new information about biostratigraphy biochronology and the evolutionary history of calcareous nannofossils across the paleocene eocene transition interval the sediment cores from odp leg 199 represent the first continuous paleocene eocene boundary sections ever to be sampled in the central equatorial pacific ocean calcareous nannofossil assemblages are studied to document the distribution of biostratigraphically useful taxa such as ericsonia discoaster fasciculithus rhomboaster and tribrachiatus focus is given to the evolution of the rhomboaster tribrachiatus lineage in the lower eocene interval at site 1215 and on the stratigraphic relationship of these taxa relative to species in the genus fasciculithus critical intervals of north atlantic dsdp site 550 have also been re examined the tribrachiatus digitalis morphotype was described at site 550 from an interval affected by down hole contamination partly originating from within the tribrachiatus orthostylus range the t digitalis morphotype represents an evolutionary transitional form between t contortus and t orthostylus entering the stratigraphic record within the range of the former species and disappearing within the lower part of the range of the latter species the subzonal subdivision of zone np10 hence collapses lithological and colour variability reflecting orbital cyclicity occur in the lower eocene of site 1215 permitting a relative astronomical age calibration of the tribrachiatus taxa the distinct rhomboaster spp discoaster araneus association also occurs in the paleo equatorial pacific ocean together with a marked decrease in diversity of fasciculithus spp site 1220 reveals a short peak abundance of thoracosphaera spp just above the p e boundary interval which probably reflects a stressed surface water environment

high resolution nannofossil biochronology of middle paleocene to early eocene at odp site 1262 implications for calcareous nannoplankton evolution abstract over the last several decades debates on the tempo and mode of evolution have centered on the question whether morphological evolution preferentially occurs gradually or punctuated i e with long periods of stasis alternating with short periods of rapid morphological change and generation of new species another major debate is focused on the question whether long term evolution is driven by or at least strongly influenced by changes in the environment or by interaction with other life forms microfossils offer a unique opportunity to obtain the large datasets as well as the precision in dating of subsequent samples to study both these questions we present high resolution analyses of selected calcareous nannofossils from the deep sea section recovered at odp site 1262 leg 208 in the south eastern atlantic the studied section encompasses nannofossil zones np4 np12 equivalent to cp3 cp10 and chrons c27r c24n we document more than 70 biohorizons occurring over an about 10 myr time interval 62 5 ma to 52 5 ma and discuss their reliability and reproducibility with respect to previous data thus providing an improved biostratigraphic framework which we relate to magnetostratigraphic information and present for two possible options of a new paleocene stratigraphic framework based on cyclostratigraphy this new framework enabled us to tentatively reconstruct steps in the evolution of early paleogene calcareous nannoplankton through documentation of transitional morphotypes between genera and or species and of the phylogenetic relations between the genera fasciculithus heliolithus discoasteroides and discoaster as well as between rhomboaster and tribrachiatus the exceptional record provided by the continuous composite sequence recovered at walvis ridge allows us to describe the mode of evolution among calcareous nannoplankton new genera and or new species usually originated through branching of lineages via gradual but relatively rapid morphological transitions as documented by the presence of intermediate forms between the end member ancestral and descendant forms significant modifications in the calcareous nannofossil assemblages are often related to significant changes in environmental conditions but the appearance of structural innovations and radiations within a single genus also occurred during stable environmental conditions these lines of evidence suggest that nannoplankton evolution is not always directly triggered by stressed environmental conditions but could be also driven by endogenous biotic control

relation between chemical composition and sedimentation rate of pacific ocean floor sediments deposited since the middle cretaceous basic evidence for chemical constraints on depositional environments of ancient sediments chemical characteristics of pacific marine sediments were examined for different environments operating since the middle cretaceous as a result of the examinations a procedure for evaluating depositional environments of ancient sediments in orogenic belts is proposed the concentration of hydrogenous authigenic elements such as mn co and ni in sediments has a relationship to the bulk sedimentation rate similarly a new indicator which is a measure of the sedimentation rate of terrigenous lithogenic materials in sediments is proposed this indicator is expressed as the weight ratio of a hydrogenous element to tio 2 because the sedimentation rate of terrigenous materials gradually decreases with distance from land the ratio varies according to depositional environments geochemical examination of pacific dsdp materials has shown that the distribution of element ratios mno tio 2 co tio 2 and others in surface sediments of the pacific has not changed since the middle cretaceous as an

calcareous nannofossil changes in response to the spreading of the south china sea basin during eocene oligocene abstract numerous models have been proposed to constrain the process of the south china sea formation yet the paleogene paleoenvironmental researches are hindered by the paucity of long continuous well dated geological records in this work eocene to oligocene nannofossil biostratigraphy and assemblage changes in a sediment section from the northern south china sea were studied to shed light on these issues we established an age model to confine the studied section between 40 and 22 ma based on 17 calcareous nannofossil datum levels the age model enabled to date the most prominent seismic reflector t60 centered at 26 8 ma a regional tectonic event interpreted as corresponding to the ridge jump event in the early phase of south china sea spreading changes in nannofossil abundance and assemblage compositions imply continuous transgression and deepening of water depth from the late eocene to early miocene during the late eocene the studied area was a neritic sea with relatively eutrophic conditions supporting abundant r lockeri group and c pelagicus from 34 ma to 27 ma during the oligocene the earlier neritic environment was replaced by relative warm and oligotrophic conditions in a shallow sea as indicated by higher concentration of c floridanus sphenolithus spp and helicosphaera spp since 26 ma pelagic conditions prevailed small reticulofenestra

hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication od ocean ridge activity adachi m yamamoto k and sugisaki r 1986 hydrothermal chert and associated siliceous rocks from the northern pacific their geological significance as indication of ocean ridge activity sediment geol 47 i25 148 analyses of 42 cretaceous rock samples from deep sea drilling project dsdp leg 32 in tile northern pacific show that chert and porcellanite are enriched in fe mn p cu ba mo ni and pb relative to both triassic biogenic cherts of central japan and cretaceous dsdp cherts of leg 62 the iron enrichment up to 6 68ve fe20 as total iron is most prominent in chert immediately overlying basal basah which is the only chert free of radiolarians and veined by megaquartz containing many fluid inclusions chemical features characterized by a low ratio for a1 ai fe mn and ai z tio 2 and a high ratio for total fe2oj tio 2 mno tio 2 and mo tio 2 as well as petrological evidence indicatc that the cherts formed in an intense submarine hydrothermal environment on or near the cretaceous japanese spreading center which separated the kula plate from the pacific plate the spreading rate of the cretaceous japanese spreading center estimated from the chemical composition of the cherts was about 3 7 cm r i the rate is comparable to that inferred from the geomagnetic data

paleogene calcareous nannofossil magnetobiochronology results from south atlantic dsdp site 516 abstract the detailed study of an expanded paleogene section with abundant moderate to well preserved calcareous nannofossils from south atlantic dsdp site 516 has resulted in a precise correlation of most calcareous nannofossil markers with the magnetostratigraphy many nontraditional datums have also been documented and correlated to the magnetostratigraphy comparison of the results from site 516 with those of previous studies from other areas enables a critical evaluation of the accuracy synchroneity or diachroneity of the species events over geographically long distances of special significance is the correlation for the first time of the stratigraphic ranges of chiasmolithus gigas and rhabdosphaera gladius with the magnetostratigraphy other important results include the following first occurrence fo of cruciplacolithus primus 66 3 ma fo chiasmolithus danicus 65 6 66 0 ma fo prinsius martinii 65 5 66 0 ma fo heliolithus kleinpellii 59 8 61 6 ma probably diachronous last occurrence lo of tribrachiatus orthostylus 51 0 54 8 ma unreliable fo chiasmolithus gigas 47 4 ma fo reticulofenestra umbilica 44 6 ma lo chiasmolithus gigas 44 4 46 8 ma diachronous lo nannotetrina fulgens 44 2 ma lo chiasmolithus grandis 40 0 41 6 ma probably diachronous fo chiasmolithus oamaruensis 39 8 40 4 ma unreliable fo isthmolithus recurvus 39 5 ma lo reticulofenestra reticulata 37 6 ma lo discoaster saipanensis 36 4 ma end acme of ericsonia subdisticha diachronous fo and lo sphenolithus distentus unreliable and lo reticulofenestra bisecta 24 0 ma

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

shelf and open ocean calcareous phytoplankton assemblages across the paleocene eocene thermal maximum implications for global productivity gradients abrupt global warming and profound perturbation of the carbon cycle during the paleocene eocene thermal maximum petm ca 55 ma have been linked to a massive release of carbon into the ocean atmosphere system increased phytoplankton productivity has been invoked to cause subsequent co2 drawdown cooling and environmental recovery however interpretations of geochemical and biotic data differ on when and where this increased productivity occurred here we present high resolution nannofossil assemblage data from a shelf section the u s geological survey usgs drill hole at wilson lake new jersey and an open ocean location ocean drilling program odp site 1209 paleoequatorial pacific these data combined with published biotic records indicate a transient steepening of shelf offshelf trophic gradients across the petm onset and peak with a decrease in open ocean productivity coeval with increased nutrient availability in shelf areas productivity levels recovered in the open ocean during the later stages of the event which coupled with intensified continental weathering rates may have played an important role in carbon sequestration and co2 drawdown

nannofossil assemblage fluctuations during the paleocene eocene thermal maximum at sites 213 indian ocean and 401 north atlantic ocean palaeoceanographic implications the paleocene eocene thermal maximum petm was an abrupt global warming event at f55 ma this event had profound effects on the biosphere quantitative investigations of calcareous nannofossil assemblages were performed across the petm at deep sea drilling project site 213 in the tropical indian ocean and site 401 in the bay of biscay north atlantic ocean at a temperate latitude calcareous nannofossil assemblages from both sites show major changes before during and after the petm fluctuations at site 213 are affected by selective dissolution of the least robust taxa by contrast assemblages in the lower part of the petm at site 401 show less diagenetic alteration and display high abundances of genera such as discoaster fasciculithus and ericsonia these taxa reflect relatively warm and probably oligotrophic surface waters abundances of the genus chiasmolithus an indicator of relatively cool and eutrophic waters decreased dramatically the upper portion of the petm is characterized by an increase in the abundance of toweius spp and zygrhablithus bijugatus interpreted as a return to cooler and more eutrophic conditions the elimination of fasciculithus was probably due to competition with the holococcolith species z bijugatus which occupied the same ecological niche the occurrences of long armed and asymmetrical discoaster species such as discoaster araneus discoaster anartios and discoaster okadai and rhomboaster species such as rhomboaster calcitrapa and rhomboaster cuspis are characteristic of the petm interval d 2004 elsevier b v all rights reserved

evidence of surface water oligotrophy during the paleocene eocene thermal maximum nannofossil assemblage data from ocean drilling program site 690 maud rise weddell sea 1 nannoplankton assemblages at ocean drilling program site 690 maud rise weddell sea experienced an abrupt and dramatic transformation at the onset of the paleocene eocene thermal maximum petm at 55 m y the major assemblage shift suggests a change from colder more productive surface waters to warmer more oligotrophic conditions significant restructuring of assemblages during the later part of the petm indicates that nannoplankton communities were not stable and that surface water conditions changed although they remained warm and oligotrophic combined with benthic foraminiferal assemblage data nannoplankton assemblage results suggest increased sequestration of nutrients in shelf environments and starvation of the open ocean although the petm was a short lived event it appears to have had long term effects on nannoplankton leading to the extinction of fasciculithus a dominant paleocene genus

coccolith sr ca records of productivity during the paleocene eocene thermal maximum from the weddell sea 1 a major perturbation of the global carbon cycle 55 million years ago believed to result from release of 1000 2000 gt of c from methane hydrates correlates with an intense but transient greenhouse warming event known as the paleocene eocene thermal maximum petm the rapid 105 years recovery of global temperatures reflects important negative feedbacks in the climate system and carbon cycle enhanced marine productivity may be one important feedback but indicators for productivity changes have yielded conflicting results here we use a new independent indicator sr ca in coccolith carbonate which covaries with the productivity of coccolithophorid algae to investigate the biotic response in the most complete petm deep sea record which was recovered at odp site 690 in the weddell sea in the dominant coccolithophorid genus toweius a large 40 sr ca increase immediately after the gas hydrate release signals a dramatic productivity increase productivity levels remained high for 60 000 years but decreased to pre event levels by 120 000 years after the gas hydrate release productivity levels during the petm are higher than observed at any other time in our 400 000 year record other coccolithophorid genera chiasmolithus and discoaster show a brief modest 25 sr ca increase increase in productivity that lags behind the methane event by 50 000 years and is within the range of productivity variation elsewhere in the record the timing of the toweius productivity increase agrees well with os isotope records of globally increased weathering intensity which may have provided higher nutrient fluxes to stimulate algal productivity if this type of productivity response occurred globally it would also be consistent with the timing of c drawdown that may have returned temperatures to near pre event levels

track deflection of typhoon nesat 2017 as realized by multiresolution simulations of a global model abstracttyphoon nesat 2017 headed west northwestward toward taiwan but took a relatively larger northward deflection about 300 km away and then a leftward deflection after landfall at northern ta

the response of calcareous nannofossil assemblages to the paleocene eocene thermal maximum at the walvis ridge in the south atlantic compositions and abundances of calcareous nannofossil taxa have been determined in a ca 170 kyrs long time interval across the paleocene eocene boundary at 1 cm to 10 cm resolution from two odp sites 1262 1263 drilled along the flank of the walvis ridge in the south atlantic the results are compared to published data from odp site 690 in the weddell sea the assemblages underwent rapid evolution over a 74 kyrs period indicating stressed unstable and or extreme photic zone environments during the petm hyperthermal this rapid evolution which created 5 distinct stratigraphic horizons is consistent with the restricted brief occurrences of malformed and or weakly calcified morphotypes the production of these aberrant morphotypes is possibly caused by major global scale changes in carbon cycling in the ocean atmosphere system affecting also photic zone environments no marked paleoecologically induced changes are observed in abundances of the genera discoaster fasciculithus and sphenolithus at the walvis ridge sites surprisingly there is no significant correlation in abundance between these three genera presumed to have had a similar paleoecological preference for warm and oligotrophic conditions

hydrothermal mn deposits of the franciscan assemblage ii isotope and trace element geochemistry and implications for hydrothermal convection at spreading centers abstract major element trace element and sr nd pb and o isotopic data for a franciscan mn deposit suggest an origin by seafloor hydrothermal circulation based on q mode factor analysis the cherts and mn lenses of the blue jay mine formed from a combination of 4 components representing 1 biogenic 1 hydrothermal and 2 detrital sources rb sr u th pb and o isotopic systematics in the mn lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts nd isotopic compositions in both cherts and mn lenses are identical and within the range measured for pacific ocean water suggesting the ree were not mobilized by hydrothermal activity correlation of 18 o with sio 2 and mno 2 in the mn lenses implies the lenses formed by simple mixing of hydrothermally derived mn oxides with seawater and biogenic silica 18 o of the cherts is both uniform and depleted relative to dsdp jurassic cherts but similar to microquartz bearing cherts of the monterey formation this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism finally a well defined rb sr isochron of 158 5myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record

early permian transform margin development of the southern new england orogen eastern australia eastern gondwana the southern new england orogen part of the eastern margin of gondwana evolved from a zone of high angle plate convergence during the carboniferous into either a transform margin or a highly oblique convergent margin by the early permian fault bounded narrow elongate rapidly filled sedimentary basins that developed along the peel manning fault system in the early permian provide support for this hypothesis they are similar to sedimentary basins developed along strike slip fault zones worldwide strike slip dislocations provide the best explanation for juxtaposition of terranes with distinctly different geological histories and discontinuities in regional geological trends across these basins a close spatial relationship also exists between occurrences of serpentinite matrix ophiolitic melange the peel manning fault system and related secondary faults early permian transtension may have facilitated the diapiric rise of serpentinites which originated from an older underlying ultramafic precursor up these fault zones rise and early permian emplacement of the bundarra plutonic suite an s type batholith across which regional geological trends are offset is also best accommodated in a model that involves a transtensional regime copyright 1992 by the american geophysical union

influences of north pacific ocean domain extent on the western u s winter hydroclimatology in variable resolution cesm author s rhoades am jones ad o brien ta o brien jp ullrich pa zarzycki cm abstract 2020 american geophysical union all rights reserved variable resolution global climate models vrgcms are a dynamical downscaling method that can reach spatiotemporal scales needed for regional climate assessments over the years several users of vrgcms have assumed where the location and extent of the refinement domain should be based on knowledge of the prevailing storm tracks and resolution dependence of important regional climate processes e g atmospheric rivers ars and orographic uplift but the effect of high resolution domain size and extent on the simulation of downstream hydroclimatic phenomena has not been systematically evaluated here we use variable resolution in the community earth system model vr cesm to perform such a test to do this three vr cesm grids were generated that span the entire two thirds and one third of the north pacific and evaluated for a 30 year climatology using atmospheric model intercomparison project protocols simulations are compared with reanalysis products offshore fifth generation of the european centre for medium range weather forecasts atmospheric reanalysis era5 and onshore livneh 2015 https doi org 10 1038 sdata 2015 42 and parameter elevation regressions on independent slopes model prism of the western united states the westward expansion of refinement domain influenced integrated vapor transport ivt which was generally high biased but minimally impacted ar characteristics due to slight differences in landfalling ar counts in the western united states california winter precipitation generally improved with westward expansion of the refinement domain western u s mountain snowpack and surface temperatures were insensitive to refinement domain size and were more influenced by changes in topographic resolution and or land surface model version given minimal dependence of simulated western u s hydroclimate on refinement domain size over the north pacific we advise future vr cesm studies to focus grid resolution on better resolving land surface heterogeneity

insights from the paleogene tropical pacific foraminiferal stable isotope and elemental results from site 1209 shatsky rise 1 stable isotope and elemental measurements were conducted on foraminifera from a sequence of calcareous pelagic ooze at ocean drilling program site 1209 to document the thermal evolution of the north pacific water column over shatsky rise and to address long standing questions about the nature of oceanic circulation in the early paleogene a major change in seasonality and water column structure in the early eocene marks a change in tropical pacific climate and circulation just prior to the early eocene climatic optimum subsequent long term cooling is interrupted by a transient positive 18o excursion identified in planktonic and benthic foraminifera during the late early eocene that is interpreted as evidence for ephemeral formation of deep water from a low latitude saline source paired analysis of benthic mg ca and 18o was undertaken to assess the relative contribution of temperature and seawater oxygen isotope composition to the benthic 18o record stratigraphic trends of benthic 18o and mg ca decouple during two intervals in the early eocene and early middle eocene although variable seawater 18o is the most likely candidate to explain decoupling of benthic 18o and mg ca it is difficult to argue for substantial change in continental ice volume during a presumably ice free interval of time

calcareous plankton evolution and the paleocene eocene thermal maximum event new evidence from tanzania the biotic response of calcareous microplankton at the paleocene eocene thermal maximum petm climate event principally comprised poleward migrations the appearance of excursion taxa and elevated turnover in calcareous nannoplankton here we examine whether this relatively muted evolutionary signal may be due to the quality of the stratigraphic and fossil record by analysing exceptionally well preserved microfossils from an expanded hemipelagic petm section in southern tanzania tdp site 14 both nannofossils and planktonic foraminifera show major abundance declines at the onset of the petm that are not explained by dilution or dissolution the petm onset is also marked by the extinction of eight nannofossil species possibly as many as 12 and the intra petm assemblages are quite distinct from background and dominated by coccolithus including the excursion taxon c bownii this biotic response is not clearly biased in favour of particular ecological groups although the nannofossil excursion taxa were all warm water favouring and there was a net diversity loss within cool water favouring eutrophic groups a shift from toweius to coccolithus dominated assemblages is suggestive of increased oligotrophy although the presence of abundant gladiolithus indicates upper photic zone oligotrophy throughout the time interval represented by the tdp site 14 section the significant plankton assemblage shifts diversity decline and possible reduction of calcareous plankton production and or export suggest the rapid onset of highly disruptive environmental change at the petm onset this change must have included rapid temperature increase and heat stress may have played a role in shaping the petm assemblage compositions causing a limited number of extinctions and favouring taxa from warmer areas of the groups ecological range however the muted evolutionary response in these plankton groups indicates that they were highly resilient to this environmental change and through adaptation to the new conditions e g the excursion taxa but probably principally through range shifts i e migration or simply the ability to acclimatize the vast majority of the biodiversity survived and thrived again once conditions returned to normal

origin and deposition of organic matter in continental chert of the middle permian gufeng formation in the northeastern yangtze platform abstract the middle permian gufeng formation in the northeastern yangtze platform china contains radiolarian chert that is characterized by black color high content of fe mo ni cu and zn based on the inorganic geochemical features previous work concluded that the cherts were deposited under sulfate reducing conditions in this study organic carbon c org n and s contents of the cherts and h c and o c ratios of kerogen were examined to explore the origin of the organic matter the concentration of c org in the black chert is extremely high relative to other cherts in accretionary complexes and continental platforms the average c n ratio of organic matter is 35 indicating that the organic matter originates from land plants the kerogen from the chert is classed as type iv based on the h c and o c ratios suggesting that oxidized or reworked organic matter was supplied to the gufeng basin therefore the organic matter is considered to originate from terrestrial plants or reworked material from land due to the depositional setting on a continental platform nutrient supplied with organic matter from land probably played an important role in abundant biogenic productivity and sedimentation of the radiolarian chert on the continental platform

geographic controls on nannoplankton extinction across the cretaceous palaeogene boundary calcareous nannoplankton a large group of marine autotrophs that produce carbonate skeletons were decimated to less than 10 of species during the cretaceous palaeogene boundary mass extinction 65 million years ago although the mass extinction followed an impact event the exact cause of the nannoplankton mortality is not well understood here we assess the timing and spatial variability of nannoplankton extinction by analysing nannofossil counts in cretaceous palaeogene boundary sections from all of the main ocean basins we find that extinction rates were higher in the northern hemisphere oceans and diversity remained low for 310 000 years in contrast southern hemisphere oceans showed lower extinction rates and a nearly immediate recovery of normal nannoplankton populations we propose that the oblique northward impact concentrated ejected particulates into the northern hemisphere blocking sunlight and suppressing photosynthesis increased rates of extinction and a prolonged recovery would then be associated with the greatest concentration of particulates we speculate that metal poisoning from fallout of the particulates may have exacerbated and extended the nannoplankton crisis in the northern hemisphere and thereby slowed the recovery of the northern hemisphere marine food web over 90 of calcareous nannoplankton species disappeared during the cretaceous palaeogene mass extinction which occurred after an impact event palaeontological analyses show that the extinction was most pronounced in the northern hemisphere oceans possibly as a result of an increased concentration of particulates created by the impact in the north

abiotic forcing of plankton evolution in the cenozoic we characterize the evolutionary radiation of planktic foraminifera by the test size distributions of entire assemblages in more than 500 cenozoic marine sediment samples including more than 1 million tests calibration of holocene size patterns with environmental parameters and comparisons with cenozoic paleoproxy data show a consistently positive correlation between test size and surface water stratification intensity we infer that the observed macroevolutionary increase in test size of planktic foraminifera through the cenozoic was an adaptive response to intensifying surface water stratification in low latitudes which was driven by polar cooling

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

paleomagnetism of red cherts a case study in the inuyama area central japan this study is an attempt to isolate and identify the primary magnetization in red cherts red chert samples from a middle triassic sequence in the inuyama area 35 4 n 137 0 e central japan have a multicomponent magnetization which is delineated by thermal demagnetization two of the components have high coercivity and high blocking temperatures one is carried by hematite and the other by magnetite the former was concluded to be the primary magnetization for two reasons 1 it predates intraformational folding and 2 it records geomagnetic reversals the other component which accounts for the dominant part of natural remanent magnetization was probably acquired at a time long after the deposition two paleomagnetic results were drawn from the middle triassic red chert sequence 1 the mean inclination of the samples in the sequence was 1 4 6 8 therefore the paleolatitude amounts to 0 7 3 4 in contrast to the paleolatitude expected from the paleopole of eurasian continent which is about 70 and 2 the magnetostratigraphy of this sequence indicates that two geomagnetic epochs in the middle triassic are considerably longer more than several million years than the average of those in the cenozoic

nannofossil evolutionary events in the mid pliocene an assessment of the degree of synchrony in the extinctions of reticulofenestra pseudoumbilicus and sphenolithus abies abstract the mid pliocene was an interval of subtle reorganisation within the nannoplankton community including the prominent and biostratigraphically important last occurrences of sphenolithus abies and reticulofenestra pseudoumbilicus the transition is part of the pliocene to recent attrition of nannofossil species that resulted from changes in the distribution of trophic resources and deep water and surface water current systems likely associated with the initiation of northern hemisphere glaciation the extinctions of sphenolithus abies and reticulofenestra pseudoumbilicus were analysed in detail at odp sites 659 662 and 926 in the equatorial and subequatorial atlantic these taxa show significantly different patterns of duration and timing of decline based on high resolution abundance records and calibration with oxygen isotope stratigraphy the initiation of abundance decline between 3 71 and 3 67 ma and the extinction of s abies between 3 56 and 3 52 ma are diachronous this extinction may have been a response to the intensification of glacial intervals at this time in contrast the last occurrence of r pseudoumbilicus at 3 81 3 82 ma appears to be a valid example of biostratigraphic although not necessarily biological synchrony in the fossil record direct environmental forcing is not attributable for the extinction of r pseudoumbilicus however indirect physical and or biological environmental stress may explain the observed patterns

controls of sea level fluctuations on the formation of ordovician siliceous nodules in terrigenous offshore environments abstract siliceous nodules of the ordovician period of the armorican massif and of southwest sardinia are made of a mixture of terrigenous origin material quartz and phyllosilicates and of biogenic origin components microcrystalline quartz calcium phosphate and calcite they are associated with fine grained sequences which were deposited between the distal part of the inner shelf and the outer shelf within these sequences two facies can be distinguished clayey silty facies without nodules related to episodes of high sedimentation rate and nodule bearing clayey facies linked to episodes of reduced sedimentation the genesis of the siliceous nodules can be integrated into a model taking account of the fluctuations in terrigenous flux due to eustatic variations during periods of rising sea level the terrigenous flux decreases and the sedimentation is dominated by bioclastic elements calcareous siliceous and phosphatic stability of the sediment water interface facilitates biogenic silica dissolution during early diagenesis silica precipitation leads to the formation of proto nodules the distribution of the two facies can be explained by the superposition of two eustatic signals one of very high frequency vhf and the other of high frequency hf the silty clayey facies could be accumulated during the period of falling sea level within the hf cycle and the nodule bearing clayey facies could correspond to amalgamation of several vhf cycles related to periods of low sedimentation rate in the hf cycle

significance of devonian carboniferous radiolarians from accretionary terranes of the new england orogen eastern australia abstract radiolarians provide age constraints for many previously undated terranes in the new england orogen neo a tectonic collage developed along the eastern margin of australia djungati terrane the age range of which was previously unknown contains two distinctive siliceous sedimentary lithofacies the oldest is a thick sequence of red ribbon bedded cherts which probably accumulated in a deep ocean floor setting far from land middle silurian through late devonian radiolarians have been recovered from these cherts green tuffaceous cherts which contain a latest devonian famennian radiolarian fauna depositionally overlie the lower red ribbon bedded chert sequence these cherts are intercalated with volcaniclastic sediments and the fauna which they contain can be used to constrain the timing of accretion of older rocks into a subduction complex anaiwan terrane which was also previously undated contains thin ribbon bedded cherts which are depositionally overlain by tuffaceous chert siliceous siltstones and volcaniclastic sediments latest devonian late famennian and early carboniferous radiolarians have been recovered from these cherts and tuffaceous siltstones radiolarians also occur in fine grained siliceous sediments of the yarrimie formation part of the gamilaroi terrane these radiolarians are of late devonian frasnian affinity and their presence indicates that blocks of limestone which contain givetian conodonts and corals and were previously thought to indicate the age of the yarrimie formation are allochthonous

structure of the havallah sequence golconda allochthon nevada evidence for prolonged evolution in an accretionary prism the golconda allochthon of northern and central nevada contains the havallah sequence and correlative units of latest devonian to early late permian age the havallah sequence is dominated by radiolarian ribbon chert and argillite associated with variable but generally subordinate siliciclastic cal carenitic and volcaniclastic turbidites and slump deposits cherts of all ages except pennsylvanian locally rest depositionally on tholeiitic basalts some were altered and mineralized by ridge type hydrothermal systems suggesting deposition in an ocean basin containing active spreading center s for much of the upper paleozoic the havallah sequence was thrust eastward along the basal golconda thrust onto coeval sediments of the western north american shelf during the latest paleozoic earliest mesozoic sonoma orogeny detailed studies of the havallah sequence in the sonoma and tobin ranges and in battle mountain indicate the presence of complex diagenetic and structural fabrics that developed prior to the obduction of the allochthon a large number of thrusts composite thrusts and shear zones slice the havallah into numerous tectonic packets of contrasting lithology and or internal structural style internal structures in chert packets include bedding parallel and bedding normal solution cleavage solution boudins three or more sets of east verging folds of variable geometry and features associated with high pore fluid pressures such as crack seal fractures dilation breccias clastic dikes and sills and clastic intrusions along thrust surfaces the fabrics suggest a general progressive evolution from deformation characterized by bedding normal compression and slight east west extension d1 to deformation dominated by bedding parallel east directed shear d2 local chert packets may have suffered alternating episodes of high and low pore fluid pressure the degree of development and the styles and orientations of various structural elements vary sometimes radically from packet to packet the pre golconda thrust fabrics can be modeled as the result of imbrication and deformation of successive batches of ocean floor sediments into the toe of an accretionary prism in front of an east facing arc relatively undeformed permian calcarenite units interpreted as being trench slope deposits suggest that this prism was well developed by permian time coarse slump deposits containing chert clasts with pre depositional structural fabrics suggest a prism that was active long enough to recycle previously tectonized cherts if we are correct the classical sonoma orogeny d3 marked the culmination of a protracted structural evolution that may have spanned much of the upper paleozoic

the micropaleontological record of marine early eocene oil shales from jordan abstract core os 28 located in central jordan offers an expanded record of calcareous nannofossils and benthic foraminifera for the early eocene of the southern tethys the oil shale succession of the studied interval covers calcareous nannofossil biozones np10 np11 np12 and np13 microfossils document the biotic response of calcareous nannofossils and benthic foraminifera to short and long term warming trends of the early eocene following the paleocene eocene thermal maximum petm on a global scale two early eocene short term shifts to higher atmospheric co 2 concentration are recorded by negative 13 c excursions these are known as eocene thermal maximum 2 and 3 etm2 etm3 stable isotope records 13 c org 13 c carb 18 o carb from the study area do not show these negative excursions which elsewhere can be correlated with the two hyperthermal events known from early eocene successions the absence of negative 13 c signals otherwise typical for etm2 and etm3 is explained by a diagenetic alteration of the isotope signal after deposition high abundances of the nannofossil taxon sphenolithus spp in biozone np10 indicate less fertile conditions for this interval than for the overlying biozone np11 throughout biozones np11 to np13 coccolithus pelagicus and toweius spp are the dominant taxa of the assemblages suggesting a mesotrophic environment surface waters experienced a temperature change from warm to moderate warm the benthic foraminifera in calcareous nannofossils biozone np10 and in the lower part of np11 reflect oligo mesotrophic and moderate to well oxygenated bottom water conditions throughout the upper part of biozones np11 np12 and np13 the benthic foraminifera are characterized by an increasing abundance of anomalinoides zitteli lenticulina spp and valvulineria scrobiculata this coincides with enriched total organic matter content toc indicating a shift to mesotrophic conditions and a moderate oxygen supply of the bottom waters based on the micropaleontological observations made in core os 28 the early eocene is first characterized by an increase and subsequently by a decrease of nutrients and oxygen the composition of both benthic and planktic communities was rather controlled by variations of regional environmental parameters than by global ones these include strong runoff climatic variability and the architecture of the basin

stratigraphy and sedimentology of jurassic bedded chert overlying ophiolites in the north apennines italy in the north apennines of italy upper jurassic bedded chert stratigraphically overlies ophiolitic rocks and is overlain by lower to middle cretaceous pelagic limestone and shale and upper cretaceous flysch the bedded chert best exposed in east liguria and on elba is typically 30 80 m thick but occasionally reaches 150 200 m thickness it consists of two main alternating lithologies siliceous mudstone sm and radiolarite r chert sections commonly show characteristic stratigraphic changes lower cherts display a striking rhythmic alternation of r and ferruginous sm beds in middle cherts sm beds are much less ferruginous and shalier intercalations are locally present in upper cherts r beds are less frequent and sm beds are essentially non ferruginous r beds are generally 1 4 cm thick and consist of 80 90 quartz 5 15 clays and usually 1 hematite they are commonly parallel laminated and rarely size graded in size graded beds large radiolaria are more abundant near the bed base commonly together with ophiolitic or sm clasts and small radiolaria more abundant near the bed top sorting is poor throughout most r beds r beds are interpreted as turbidites cf nisbet price 1974 model calculations suggest that typical settling velocities of radiolaria during redeposition are 1 cm sec 1 which is low and of restricted range relative to the 1 10 cm sec 1 settling velocities of clastic grains of comparable size range radiolaria therefore should have only a limited tendency to grade and sort during deposition from a turbulent current sm beds are commonly 1 7 cm thick although much thicker ones occur near the base of sections and consist mainly of 50 70 quartz 15 35 clays and 0 15 hematite microscopic clay silica aggregates and highly corroded remnants of radiolaria are common sm beds are interpreted as mainly ambient pelagic sediment which accumulated slowly in topographic lows and which was modified by near surface dissolution of biogenic silica in sm beds which contain two texturally different layers the lower one is interpreted as the top of the underlying radiolarian turbidite north apennine cherts represent the first sediment deposited on oceanic crust formed during the opening of the north apennine part of the tethys the ophiolitic basement had a rugged topography which favoured the redeposition of siliceous sediment hematite and local mn enrichments in sm beds in the lower chert sections represent hydrothermal precipitates inferred to have originated at a spreading axis during seafloor spreading accumulation of siliceous sediments progressively reduced the topography deposition of ophiolitic detritus within the sediments phased out during early chert sedimentation and the hydrothermal contribution during early middle chert sedimentation as local basins filled during late chert sedimentation radiolarian turbidites became less frequent the first limestones at the top of chert sections are calcareous ooze turbidites derived from above the ccd and deposited slightly below it gradual descent of the ccd to ocean floor depths at the end of the jurassic bosellini winterer 1975 led to the replacement of siliceous by carbonate sedimentation

accordion vs quantum tectonics insights into continental growth processes from the paleozoic of eastern gondwana the early paleozoic lachlan fold belt of eastern australia is widely regarded as an ancient convergent plate margin beneath which paleo pacific panthalassic oceanic lithosphere was continuously subducted it is cited as the type example of a retreating accretionary orogeny however sandstone compositions the sedimentological nature and timing of chert accumulation and overall stratigraphic architecture are not necessarily consistent with this model we suggest an alternative explanation for growth of gondwanan continental margin oceanic lithosphere outboard of the passive gondwana continental margin was subducted beneath an extensive intra oceanic island arc that now crops out as an allochthonous element macquarie arc within the fold belt once intervening oceanic lithosphere was eliminated this arc collided with and was emplaced upon the gondwana margin recognition of four such events along this margin through the phanerozoic suggests it is a significant mechanism for continental growth

tectonic setting and paleoenvironment of terranes in the southern new england orogen eastern australia as constrained by radiolarian biostratigraphy abstract radiolarians are abundant in the gamilaroi djungati and anaiwan terranes of the new england orogen in eastern australia these microfossils present the first age constraints on the timing of development of hitherto undated lithologies within the various juxtaposed terranes of the orogen they give a biostratigraphic framework for interpreting the history of marine sedimentation in these terranes and have significant implications for published tectonic models radiolarians also show that the stratigraphically lowermost rocks of the gamilaroi terrane are most probably of devonian age better stratigraphic resolution permits interpretation of these rocks as part of an intra oceanic island arc succession which accreted to the eastern margin of australia gondwana around the end of the devonian this intra oceanic arc is distinct from a younger carboniferous superposed continental arc sequence which constitutes a successor basin that developed over the gamilaroi terrane subsequent to its accretion to the margin of australia radiolarians provide the basis for dating siliceous lithologies which dominate the djungati terrane and permit a more detailed analysis of the history of this terrane during the middle silurian through late devonian the djungati terrane was part of an oceanic basin which was isolated from any source of terrigenous sedimentation the djungati terrane was subsequently influenced by volcanic island arc activity and was tectonically disrupted during the latest devonian to early carboniferous radiolarian age data show that age correlations inferred on the basis of similarities in detrital sandstone petrography between lithostratigraphic units in the gamilaroi and djungati terranes are not always appropriate djungati terrane has been widely interpreted as a subduction complex related to the gamilaroi terrane radiolarian data now elucidate much of the structural complexity of this terrane significant differences between the djungati terrane and the style of well documented subduction complexes include the close spacing of zones of radiolarian chert the dominance of this lithology over others and the lateral extent of many of the chert horizons the anaiwan terrane has features which are characteristic of many well documented subduction complexes radiolarians are abundant in this terrane and can be used to show that it developed along the eastern margin of australia in response to early carboniferous subduction of late devonian to early carboniferous oceanic crust packages of chert accreted into the subduction complex are progressively younger towards the northeast indicating that subduction was directed to the southwest

diagenetic controls on the structural evolution of siliceous sediments in the golconda allochthon nevada u s a abstract a model is proposed that links the diagenesis of siliceous sedimentary rocks with deformation to explain the heterogeneous structural fabric of radiolarian cherts in the upper paleozoic golconda allochthon of nevada u s a numerous thrust faults slice the cherts into packets each with a unique set of internal structures fold geometries boudin profiles pressure solution features etc vary from packet to packet and layer to layer analogous variations in the diagenetically mixed siliceous sediments of the miocene monterey formation california suggest the cherts of the golconda allochthon were similarly mixed when they were deformed radiolarian sediments composed of biogenic silica opal a developed ductile structures and pressure solution features because of their high porosity weak lithification and the high solubility of disordered silica lowporosity strongly lithified relatively insoluble quartz cherts the final product of silica diagenesis deformed in a brittle fashion and developed fewer pressure solution features diagenetically intermediate ct cherts and ct porcelanites exhibited transitional behavior mixed diagenetic zones produced structures with layer by layer changes in structural style the dehydration of opal a and opal ct helped create the excess pore fluid pressures responsible for thrust faults hydraulic fractures dilation breccias and elastic intrusions the presence of ductile structures and numerous pressure solution features in the oldest cherts of the havallah sequence suggests that these cherts were deformed while diagenetically immature possibly within a long lived upper paleozoic accretionary prism

a geochemical study of metabasalts from a subduction complex in eastern australia abstract east of the peel fault system in the new england fold belt of eastern australia a base faulted sequence of mafic igneous rocks conformably overlain by chert siltstone and minor sandstone occurs in repeated slices forming a stacked sequence tens of kilometres thick the mafic rocks show extensive mineralogical alteration but apart from the highly mobile alkali elements bulk whole rock compositions retain a strong igneous imprint two metabasalt groups are recognised group a shows a distinct tholeiitic fractionation trend with increasing feo tio 2 p 2 o 5 feo mgo zr and y relative to only a small increase in sio 2 the mean concentration of incompatible and immobile elements and the composition of relict endiopsidic and augitic pyroxenes is similar to mid ocean ridge tholeiites particularly the more evolved ferrobasalts group b metabasalts are alkalic in composition they tend to have higher al 2 o 3 mgo p 2 o 5 and zr and lower feo and sr than group a basalts relict pyroxenes have high ti and al concentrations and are salites these rocks were probably the product of oceanic within plate volcanism both groups represent fragments of oceanic crust incorporated into a subduction complex along the eastern margin of the australian continent

mechanism of sedimentation of rhythmically bedded chert abstract the biogenic chert shale sequences in the upper paleozoic and lower mesozoic inner chichibu terrain and in the tertiary setogawa terrain formed on a bank or in the central part of a marginal sea adjacent to a nearby land the rhythmic layering results from periodic turbidity currents in spicule radiolarian bedded cherts of the inner chichibu terrain most chert beds are of symmetrical triple layered type composed of a middle siliceous layer and upper and lower argillaceous layers the amounts of hydrogenous base metals such as fe mn cu ni v and zn are higher in chert than in shale partings the mno al 2 o 3 ratio and sedimentation rate diagram in fig 4 shows that the average sedimentation rate is 7 1 m m y 1 for chert and 45 m m y 1 for shale partings these lines of evidence suggest that the shale partings formed from distal turbidity currents and are interbedded with hemipelagic biogenic chert on the other hand in the tertiary diatomaceous bedded cherts of the setogawa terrain most sets of chert beds and overlying shale partings were deposited as siliceous turbidites like in many bedded cherts in other orogenic belts of the world the frequency of occurrence of such periodic turbidity currents is calculated as one per 11 200 17 700 yrs in the inner chichibu terrain and one per 2600 10 000 yrs in the setogawa terrain

environmental perturbations at the early eocene etm2 h2 and i1 events as inferred by tethyan calcareous plankton terche section northeastern italy several early eocene hyperthermals have been recently investigated and characterized in terms of temperature anomalies and oceanographic changes the effects of these climatic perturbations on biotic communities are much less constrained here we present new records from the terche section northeastern italy that for the first time integrates data on planktic foraminifera and calcareous nannofossils across three post paleocene eocene thermal maximum petm negative carbon isotope excursions cies the bio magnetostratigraphic framework generated at terche allows us to confidently relate such cies to the eocene thermal maximum 2 etm2 h2 and i1 events each of these events coincides with lithological anomalies characterized by significantly lower calcium carbonate content marly units mus we interpret these mus as mainly linked to an effect of increased terrigenous dilution as dissolution proxies do not display significant variations calcareous plankton assemblages change significantly across these events and radiolarians increase observed changes suggest that transient warming and environmental perturbations though more intense during etm2 occurred during each of the three investigated perturbations variations among calcareous plankton suggest increase in surface water eutrophication with respect to the pre events conditions coupled with a weakening of the upper water column thermal stratification higher nutrient discharge was related to intensification of the hydrological cycle as a consequence of the warmer climate these conditions persisted during the early cie recovery implying slower recovery rates for the environment and biota than for the carbon cycle

variations in the oceanic vertical carbon isotope gradient and their implications for the paleocene eocene biological pump 1 variations in the efficiency of the biological pumping of carbon from the surface to the deep ocean have been invoked to explain changes in atmospheric pco2 and thus climate on a variety of timescales we compiled published paleocene and eocene foraminiferal carbon isotope data and adjusted them to a uniform timescale to investigate changes in the biological pump in the early cenozoic eight basinal time series were binned into 0 01 ma increments and five water column depth horizons the carbon isotope data reveal remarkably coherent trends in surface thermocline and deep water carbon isotope values through the paleocene and eocene these data were used to drive a three box ocean carbon isotope model to estimate long term relationships among changes in atmospheric pco2 organic and inorganic carbon burial and biological pumping our model results provide evidence for two different modes of organic carbon cycling during the paleocene and earliest eocene atmospheric pco2 drawdown was driven externally by terrestrial organic carbon burial after the earliest eocene variations in atmospheric pco2 resulting from imbalances in organic carbon cycling appear to have been driven by variations in the biological pump a temporary decline in biological pump efficiency at 50 ma may have led to increased atmospheric pco2 increased weathering and nutrient delivery to the oceans and enhanced organic carbon burial thus a biological pump driven increase in atmospheric pco2 created a counterintuitive inverse relationship between organic carbon burial and atmospheric pco2 with no indication of the burial event in the surface water carbon isotope record

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton