the paleocene eocene transition at mead stream new zealand a southern pacific record of early cenozoic global change mead stream in marlborough new zealand exposes a spectacular 650 m thick stratigraphic section of well bedded micritic limestone chert and marl that was deposited on a south pacific upper continental slope from late cretaceous to middle eocene the 200 m upper paleocene lower eocene succession was examined for its lithology bulk carbonate carbon isotopes and assemblages of radiolarians calcareous nannoplankton and foraminifera so that it could be placed into a global context the interval displays several prominent carbon isotope anomalies and is correlated with south pacific radiolarian zones rp5 to rp9 and calcareous nannofossil zones np6 8 to np12 additionally planktic foraminiferal zones p4 to p6b are identified in uppermost paleocene and lower eocene strata mead stream has a near continuous paleocene lower eocene sediment record and three globally significant climate events the late paleocene carbon isotope maximum pcim the initial eocene thermal maximum ietm and the early eocene climatic optimum eeco have obvious expressions the pcim is a 50 m thick interval of biosiliceous micritic limestone in which 13c is 3 the lower part contains two organic rich biosiliceous mudstone units that may represent expansion of an oxygen minimum zone omz during a global increase in marine biological productivity the ietm is a 4 m thick interval in which 13c drops below 1 5 in a pattern seen at other locations the basal 2 4 m is a distinctive recessed marl rich unit that is defined herein as the dee marl the ietm is marked by a rapid decline in the nannoplankton genus fasciculithus short lived occurrences of discoaster cf araneus and morozovella aequa aequa and significant radiolarian faunal turnover owing to impoverished benthic faunas the benthic foraminiferal extinction event bfee is poorly defined the onset of the eeco is marked by a 1 negative 13c excursion a transition from limestone rich to marl rich facies and a marked decrease in radiolarian abundance compacted sedimentation rates vary between 1 4 2 7 cm kyr for upper paleocene lower eocene strata at mead stream although individual beds with average thickness of 10 cm were deposited too fast to directly represent cycles in orbital parameters time series analysis of bed thicknesses suggests that groups of beds may record milankovitch scale periodicity perhaps with a significant obliquity component thus the relative frequency and thickness of marl and limestone beds in this section is shown to be strongly influenced by climatic changes at a wide range of temporal scales from suborbital and orbital cycles to aberrant short term events and long term trends predominance of marl in ietm and eeco intervals indicates that episodes of extreme global warming resulted in reduced oceanic productivity and increased terrestrial discharge in the high latitude southwestern pacific

comment on 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps by knight et al earth planet sci lett 208 2003 85 99 abstract knight et al presented age and chemical data on two sets of lava flows from the rajahmundry area on either bank of the godavari river the age and petrogenesis of these flows and their possible link to sections of the main deccan province are of importance to the understanding of many aspects of flood basalt volcanism i comment on a the use of geochemical fingerprints for lava identification correlation at rajahmundry superceding apparent field relations b their 40 ar 39 ar data and its refinement based on statistical tests and the alteration state of the samples c correlation of age data and the magnetic polarity of the lavas to the geomagnetic polarity time scale and d the possibility that both lavas at rajahmundry were formed by intracanyon flows derived from 1000 km away

determination of rapid deccan eruptions across the cretaceous tertiary boundary using paleomagnetic secular variation 2 constraints from analysis of eight new sections and synthesis for a 3500 m thick composite section 1 the present paper completes a restudy of the main lava pile in the deccan flood basalt province trap of india chenet et al 2008 reported results from the upper third and this paper reports the lower two thirds of the 3500 m thick composite section the methods employed are the same i e combined use of petrology volcanology chemostratigraphy morphology k ar absolute dating study of sedimentary alteration horizons and as the main correlation tool analysis of detailed paleomagnetic remanence directions the thickness and volume of the flood basalt province studied in this way are therefore tripled a total of 169 sites from eight new sections are reported in this paper together with the results of chenet et al 2008 these data represent in total 70 of the 3500 m combined section of the main deccan traps province this lava pile was erupted in some 30 major eruptive periods or single eruptive events see each with volumes ranging from 1000 to 20 000 km3 and 41 individual lava units with a typical volume of 1300 km3 paleomagnetic analysis shows that some sees with thicknesses attaining 200 m were emplaced over distances in excess of 100 km both likely underestimates due to outcrop conditions and up to 800 km the total time of emission of all combined sees could have been much less than 10 ka with most of the time recorded in a very small number of intervening alteration levels marking periods of volcanic quiescence so called big red boles the number of boles thickness of the pulses and morphology of the traps suggest that eruptive fluxes and volumes were larger in the older formations and slowed down with more and longer quiescence periods in the end on the basis of geochronologic results published by chenet et al 2007 and paleontological results from keller et al 2008 we propose that volcanism occurred in three rather short discrete phases or megapulses an early one at 67 5 1 ma near the c30r c30n transition and the two largest around 65 1 ma one entirely within c29r just before the k t boundary the other shortly afterward spanning the c29r c29n reversal we next estimate sulfur dioxide likely a major agent of environmental stress amounts and fluxes released by sees they would have ranged from 5 to 100 gt and 0 1 to 1 gt a respectively over durations possibly as short as 100 years for each see the chemical input of the chicxulub impact would have been on the same order as that of a very large single pulse the impact therefore appears as important but incremental neither the sole nor main cause of the cretaceous tertiary mass extinctions

dissociation of oceanic methane hydrate as a cause of the carbon isotope excursion at the end of the paleocene isotopic records across the latest paleocene thermal maximum lptm indicate that bottom water temperature increased by more than 4 c during a brief time interval 104 years of the latest paleocene 55 6 ma there also was a coeval 2 to 3 excursion in the 13c of the ocean atmosphere inorganic carbon reservoir given the large mass of this reservoir a rapid 13c shift of this magnitude is difficult to explain within the context of conventional hypotheses for changing the mean carbon isotope composition of the ocean and atmosphere however a direct consequence of warming bottom water temperature from 11 to 15 c over 104 years would be a significant change in sediment thermal gradients and dissociation of oceanic ch4 hydrate at locations with intermediate water depths in terms of the present day oceanic ch4 hydrate reservoir thermal dissociation of oceanic ch4 hydrate during the lptm could have released greater than 1 1 to 2 1 1018 g of carbon with a 13c of approximately 60 the release and subsequent oxidation of this amount of carbon is sufficient to explain a 2 to 3 excursion in 13c across the lptm fate of ch4 in oceanic hydrates must be considered in developing models of the climatic and paleoceanographic regimes that operated during the lptm

the cretaceous tertiary extinction modeling carbon flux and ecological response 1 it is widely recognized that a significant negative excursion in carbon isotopic 13c differences between planktic and benthic foraminiferal tests occurred at the cretaceous tertiary k t boundary we applied parametric and nonparametric breakpoint tests and statistical comparisons of different recovery models to assess the timing and pattern of recovery from this negative excursion at south atlantic deep sea drilling project dsdp site 528 and equatorial pacific dsdp site 577 our results indicate a two stage recovery with an initial recovery to an intermediate state of planktic to benthic 13c differences followed by a discontinuous shift to a final state with planktic to benthic 13c differences similar to preextinction values the final discontinuous shift in both the pacific and atlantic ocean sites occurred several million years after the k t collapse of planktic to benthic 13c differences both the first and second stages of recovery are best described by damped exponential relaxations the pattern and timing of this carbon cycle recovery may have been contingent on the occurrence of key biological events

paleogene stable isotope events the oxygen isotope record in paleogene benthic foraminifera shows that at the base of the paleogene the ocean deep waters had a temperature of about 10 c rising to about 12 c at the base of the eocene and cooling between 51 ma and 49 ma to about 9 c the most dramatic event occurred just after the eocene oligocene boundary at about 35 8 ma when ocean deep waters cooled by several degrees within 104 105 yr probably in association with temporary glaciation in the antarctic region another more intense glacial event in antarctica may have occurred later in the oligocene at about 31 ma and a third near the top of the oligocene at 24 ma in the marine carbon isotope record a very rapid negative excursion occurred precisely at the cretaceous tertiary boundary a recovery to unusually positive values in the late paleocene was followed by a second negative excursion close to the paleocene eocene boundary that was even more extreme in magnitude although it was not as rapid these major carbon isotope events permit very accurate stratigraphic correlation there are many other smaller features in the carbon isotope record that will also prove useful for this purpose

chemostratigraphic evidence of deccan volcanism from the marine osmium isotope record continental flood basalt cfb volcanism is hypothesized to have played a causative role in global climate change and mass extinctions uncertainties associated with radiometric dating preclude a clear chronological assessment of the environmental consequences of cfb volcanism our results document a 25 decline in the marine 187 os 188 os record that predates the cretaceous tertiary boundary ktb and coincides with late maastrichtian warming we argue that this decline provides a chemostratigraphic marker of deccan volcanism and thus constitutes compelling evidence that the main environmental consequence of deccan volcanism was a transient global warming event of 3 to 5 c that is fully resolved from the ktb mass extinction

oceanographic and climatic implications of the palaeocene carbon isotope maximum we have compared detailed planktonic and benthonic foraminiferal carbon and oxygen isotope records from the palaeocene and early eocene successions at dsdp site 577 shatsky rise north pacific a composite section derived from dsdp leg 74 sites walvis ridge south atlantic and a composite section from odp leg 113 sites maud rise weddell sea the 13c records of palaeocene and early eocene foraminifera at site 577 and the leg 74 sites show that an increase in 13c values in surface waters at 64 ma end of zone p1 resulted in increased vertical carbon isotope gradients 13c between surface and deeper dwelling planktonic foraminifera and between surface dwelling planktonics and benthonic foraminifera which became progressively steeper until the iniddle late palaeocene zone p4 this steepening also occurs in the latest palaeocene of the composite leg 113 section and can be explained by an increase in surface ocean productivity this increase in productivity probably resulted in an expansion of the oxygen minimum zone omz benthonic 13c values increased during the late palaeocene in site 577 and the composite leg 74 section suggesting that the palaeocene carbon isotope maximum was composed of both within ocean reservoir increased surface water productivity and between reservoir organic carbon burial ftactionation effects the benthonic 13c increase lags the surface ocean 13c increase in the early palaeocene 63 64 ma suggesting that surface water productivity increase probably led an increase in the burial rate of organic carbon relative to carbonate sedimentation moreover inter site 13c comparisons suggest that the locus of deep to intermediate water formation for the majority of the palaeocene and the earliest eocene was more likely to have been in the high southern latitudes than in the lower latitudes oxygen isotope data show a decline in deeper water temperatures in the early and early late palaeocene followed by a temperature increase in the late palaeocene and across the palaeoceneeocene boundary we speculate that these changes in deeper water temperatures were related to the flux of co2 between the oceans and the atmosphere through a mechanism operating at the high southern latitudes

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

evidence for orbital forcing of dust accumulation during the early paleogene greenhouse the accumulation of wind blown eolian dust in deep sea sediments reflects the aridity humidity conditions of the continental region supplying the dust as well as the gustiness of the climate system detailed studies of pleistocene glacial interglacial dust fluxes suggest changes in accumulation rates corresponding to orbital variations in solar insolation milankovitch cycles while the orbital cycles found in sedimentary archives of the pleistocene are intricately related to glacial growth and decay similar global orbital signals recognized in deep sea sediments of early paleogene age the last major greenhouse interval 65 45 million years ago could not have been linked to the waxing and waning of large ice sheets thus orbital signals recorded in early paleogene sediments must reflect some other climate response to changes in solar insolation to explore the potential connection between orbital forcing and the climate processes that control dust accumulation we generated a high resolution dust record for 58 myr old sediments from shatsky rise odp site 1209 paleolatitude 15 n 20 n the dust accumulation data provide the first evidence of a correlation between dust flux to the deep sea and orbital cyclicity during the early paleogene indicating dust supply responded to insolation forcing during the last major interval of greenhouse climate furthermore the relative amplitude of the dust flux response during the early paleogene greenhouse was comparable to that during icehouse climates thus subtle variations in solar insolation driven by changes in earth s orbit about the sun may have had a similar impact on climate during intervals of overall warmth as they did during glacial interglacial states

paleocene oceanography of the eastern subtropical indian ocean an integrated magnetobiostratigraphic and stable isotope study of odp hole 761b wombat plateau surface and deep water circulation patterns in the eastern indian ocean during the paleocene epoch are inferred based on an integrated magnetobiostratigraphic and stable isotope investigation of ocean drilling program hole 761b drilled on the wombat plateau a combination of magnetostratigraphy biostratigraphy and isotope stratigraphy demonstrates that numerous deep sea sites that have been considered to show continuous or nearly continuous sedimentation through the paleocene are punctuated by a series of hiatuses some of which exceeding a duration of 1 myr therefore our study is based on a detailed temporal interpretation of the stratigraphic successions we used for paleoceanographic reconstructions we compare detailed planktonic and benthic foraminiferal carbon and oxygen isotope records from hole 761b with several temporally correlative records published from different oceanic provinces in order to distinguish between local and global patterns within the eastern indian ocean although site 761 was situated at low latitudes during the paleocene its surface waters were predominantly influenced by circulation originating from the southern ocean as indicated by inferred cool sea surface temperatures and reduced surface to deep water temperature gradients we suggest that deep waters in the eastern indian ocean were not directly fed by the southern or tethys oceans rather the more negative n 13 c composition of the bottom waters recorded by benthic foraminifera implies the presence and or active contribution of aged deep waters from the pacific during this time at least prior to v60 2 ma and subsequent to v59 0 ma the indian continent ninetyeast ridge kerguelen plateau and broken ridge may have played a significant role as submarine barriers to deep water circulation during the paleocene 2002 elsevier science b v all rights reserved

effective medium modeling of velocity dispersion and attenuation in isotropic rocks abstractcalculation of the velocity of elastic waves that propagate in saturated rocks is complicated by many dispersion and attenuation mechanisms wave induced fluid flow at pore and mesoscopic scales is responsible for substantial dispersion and attenuation effects in addition dispersion and attenuation phenomena in rocks are due to spatial heterogeneities in density and elastic properties whenever the wavelength of a propagating wave is of the same scale as the size of the pores dispersion takes place in the form of multiple scattering we have developed an effective medium model that reproduced the combined effects on acoustic velocities of four wave attenuation mechanisms by replicating results predicted by existing models in saturated isotropic rocks biot s and squirt flow and acoustic scattering from spherical pores and randomly oriented penny shaped cracks first the strengthening of rocks and wave velocity increase with frequency associated with fluid related dispersion was modeled by int

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

an early eocene carbon cycle perturbation at 52 5 ma in the southern alps chronology and biotic response an early eocene carbon cycle perturbation at 52 5 ma from the southern alps chronology and biotic response

transient ocean warming and shifts in carbon reservoirs during the early danian the palaeocene eocene thermal maximum petm at 55 ma marks the palaeocene eocene p e boundary and represents a discrete period of abrupt transient global warming there are few vegetation records from within the petm and such an absence of data prevents modelling of the vegetation response to climate warming outcrops exposing the sentinel butte member upper fort union formation and the golden valley formation bear den and lower camels butte members within the williston basin of western north dakota usa are known to span the p e boundary pollen and spore floras at the farmers butte locality stark county north dakota 46 92 n 102 11 w record changes in abundance of some reed fern and understorey plants across the sentinel butte bear den contact but no other composition changes occur until the arrival of eocene immigrants platycarya spp walnut pecan family and intratriporopollenites instructus linden sterculia cotton tree families at the top of the bear den member c 11 m above the change in co occurrence and relative abundance patterns of range through taxa the exact stratigraphic level at which these eocene marker taxa first occur is unclear owing to the heavily weathered nature of bear den strata below the alamo bluff lignite this pattern of stratigraphic change may be correlative to the well documented floral gap of petm records in wyoming though bulk 13corg ratios decrease by 2 4 across the alamo bluff lignite degradation of organic carbon within the upper bear den member partially masks full expression of the carbon isotope excursion associated with the petm hence strata around the alamo bluff lignite may represent a new terrestrial record of the petm in agreement with terrestrial petm records from other u s western interior localities palynological data indicate no floral extinction and little composition change across the palaeocene eocene boundary

a complete high resolution paleocene benthic stable isotope record for the central pacific odp site 1209 1 we have compiled the first stratigraphically continuous high resolution benthic foraminiferal stable isotope record for the paleocene from a single site utilizing cores recovered at pacific odp site 1209 the long term trend in the benthic isotope record suggests a close coupling of volcanic co2 input and deep sea warming over the short term the record is characterized by slow excursions with a pronounced periodic beat related to the short 100 kyr and long 405 kyr eccentricity cycle the phase relationship between the benthic isotope record and eccentricity is similar to patterns documented for the oligocene and miocene confirming the role of orbital forcing as the pace maker for paleoclimatic variability on milankovitch time scales in addition the record documents an unusual transient warming of 2 c coeval with a 0 6 carbon isotope excursion and a decrease in carbonate content at 61 75 ma this event which bears some resemblance to eocene hyperthermals marks the onset of a long term decline in 13c the timing indicates it might be related to the initiation of volcanism along greenland margin

40k 40ar dating of the main deccan large igneous province further evidence of ktb age and short duration most mass extinctions coincide in time with outpourings of continental flood basalts cfb some 20 years ago it was shown courtillot v besse j vandamme d montigny r jaeger j j cappetta h 1986 deccan flood basalts at the cretaceous tertiary boundary earth planet sci lett 80 361 374 courtillot v feraud g maluski h vandamme d moreau m g besse j 1988 deccan flood basalts and the cretaceous tertiary boundary nature 333 843 846 duncan r a pyle d g 1988 rapid eruption of the deccan flood basalts at the cretaceous tertiary boundary nature 333 841 843 that the age of the deccan traps was close to the cretaceous tertiary kt boundary and its duration under 1 myr we have undertaken a new geochronological study using the unconventional 40k 40ar cassignol gillot technique which is particularly well suited to the potassium poor deccan lavas the mean of 4 determinations from the topmost ambenali and mahabaleshwar formations is 64 5 0 6 ma they straddle the c29r c29n reversal boundary for which they provide a new constraint the mean age of 3 determinations from the oldest jawhar formation is 64 8 0 6 ma the difference in age between top and bottom of a 3500 m composite section probably comprising 80 of the total deccan volume is statistically insignificant with the overall mean age being 64 7 0 6 ma n 7 our results are consistent with the most recent 40ar 39ar determinations knight k b renne p r halkett a white n 2003 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps earth planet sci lett 208 85 99 knight k b renne p r baker j waight t white n 2005 reply to 40ar 39ar dating of the rajahmundry traps eastern india and their relationship to the deccan traps discussion by a k baksi earth planet sci lett 239 374 382 confirming that there should be no systematic difference between the two methods when they are used in an optimal way an earlier smaller but significant pulse of volcanism between 68 and 67 ma extending over at least 500 km in latitude in the northern part of the deccan cfb has also been identified after 2 to 3 ma of quiescence the second major phase of volcanism occurred near 65 ma expanding over most of the area covered by the first pulse and another 500 km to the south consistent with drift of india by 300 to 450 km at not vert similar 150 mm yr during the quiescence period new paleontological data from the remote rajahmundry section keller g adatte t gardin s bartolini a bajpai s humler e in prep the cretaceous tertiary boundary in deccan traps of the krishna godavari basin of southeastern india epsl to be submitted suggest that this second pulse can itself be divided into two major pulses one starting in c29r and ending at the kt boundary the second starting in the upper part of c29r and ending within c29n

depth dependency of the paleocene eocene carbon isotope excursion paired benthic and terrestrial biomarker records ocean drilling program leg 208 walvis ridge 1 the paleocene eocene thermal maximum petm coincided with a negative carbon isotope excursion cie in carbonate and organic matter in terrestrial and marine records consequently the petm global warming of 5 6 c has been attributed to the rapid emission of a large amount of isotopically light carbon into the ocean atmosphere system and the magnitude of the cie has been used to estimate the amount of carbon greenhouse gas emitted however there are large discrepancies between the magnitude of the cie in marine and in terrestrial material in different types of marine carbonate records bulk carbonate planktic and benthic foraminiferal carbonate and in marine carbonate records from different locations the marine carbonate record of the cie may be incomplete in most deep sea bathyal abyssal locations because of ocean acidification and widespread dissolution of seafloor carbonates we demonstrate that the cie in benthic foraminiferal stable isotope records is relatively abrupt and not as gradual as portrayed in bulk carbonate records along the walvis ridge depth transect se atlantic the benthic cie is about 1 5 at 3600 m paleodepth in contrast to about 3 5 at 1500 m paleodepth consistent with depth dependent truncation by carbonate dissolution strong covariance between the benthic record and the stable carbon isotope values of terrestrial n alkanes isolated from the same core i e site 1263 supports a relatively rapid excursion of at least 3 5 but no more than 5 0

the calcareous nannofossil response to the end cretaceous warm event in the tropical pacific abstract the response of calcareous nannofossils to the end cretaceous warming is investigated in the tropical pacific dsdp site 577a shatsky rise through the record of species richness shannon diversity distribution patterns and statistical treatments this event is marked by a strong acme of the tropical species micula murus and is accompanied by a decrease of placozygus spiralis the disappearance of biscutum constans and a decrease in bulk 13c indicative of a decrease in primary productivity an increase in abundance of other micula species at site 577a and a drop in species richness recorded in all sites of shatsky rise suggest stressed environmental conditions coincident with the end cretaceous warming the acme of m murus at shatsky rise and in the atlantic ocean is recorded within magnetochron c29r and correlates 1 with the intense warming as expressed in intermediate waters through the 18o of benthic foraminifera and in surface waters through poleward migration reduced diversity and dwarfism in planktonic foraminifer assemblages 2 with a sharp decline in marine 187os 188os chemical marker of deccan volcanic activity and 3 with a rise in the atmospheric pco2 record of terrestrial plants in texas usa probably triggered by deccan volcanic degassing however a drop of calcareous nannofossil cool water taxa in the equatorial and south atlantic as well as a first rise in abundance of m murus in the south atlantic and tropical pacific occur in the topmost part of chron c30n and correlates with the rise in palaeotemperature record of terrestrial plants in north dakota usa this suggests that initiation of the warming in the atmosphere and surface waters may predate the striking warming of intermediate water masses by 150 200 kyr the coincidence and the links between climate change volcanism geochemical and biotic events at the end of the maastrichtian thus remain to be fully elucidated

barium and the late paleocene δ13c maximum evidence of increased marine surface productivity deep sea sediment ba ba al2o3 sample 15 ba aluminosilicate records show increasing values synchronous with the evolution of the late paleocene global 13c maximum reflecting an increase in marine surface primary production and biogenic barite formation at this time at two oligotrophic locations deep sea drilling project dsdp sites 384 and 527 in the north and south atlantic respectively ba increases from 160 360 ppm in the early paleocene to 1100 3000 ppm during the 13c maximum at equatorial dsdp site 577 positioned within or near the high productivity zone ba increases from 15 500 ppm in the early paleocene to 25 400 ppm in conjunction with late paleocene maximum 13c values linear fitted correlation plots of sediment ba content versus surface water 13c in all three regions support barite originating in the euphotic zone the early to late paleocene relative increase in ba illustrates how burial rates of corg relative to al2o3 accelerated by a factor of 1 8 and 6 0 in the eutrophic and oligotrophic areas respectively a tentative estimate weighing our result for the entire ocean suggests that accumulation rates of organic carbon increased by a factor of 2 during the late paleocene 13c maximum

volatile fluxes during flood basalt eruptions and potential effects on the global environment a deccan perspective abstract we examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time characteristically a few million years within this period a short lived climactic phase that lasts about 1 ma typically emplaces a large proportion of the lava volume this phase consists of a series of huge eruptions each yielding 10 3 10 4 km 3 of magma each eruption lasted on the order of a decade or more and built an immense p hoehoe dominated lava flow field by eruptive activity along fissures tens to hundreds of km long high fire fountains emanating from vents along the fissures at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas the combination of large eruption magnitudes maintained high effusion rates during eruptions and the repeated nature of the characteristic large scale eruptive activity occurs in earth history only during periods of flood basalt volcanism based on recent analogs and determination of volatile contents of ancient flood basalt lavas we estimate that individual eruptions were capable of releasing 10 000 tg of so 2 resulting in atmospheric loadings of 1000 tg a 1 during a sustained decade long eruptive event we apply this model of flood basalt volcanism to estimate the potential mass of co 2 and so 2 released during formation of the 65 ma deccan province the deccan lava pile contains the record of hundreds of enormous p hoehoe flow fields erupted within a period of about 1 ma consequently atmospheric perturbations associated with so 2 emissions from just one of these long lasting eruptions were likely to have been severe and constantly augmented over a decade or longer by contrast the amounts of co 2 released would have been small compared with the mass already present in the atmosphere and thus much more limited in effect individual eruptions were followed by hiatuses of hundreds to thousands of years during which the gas contributions to the atmosphere would be recycled it is clear that the nature and potential atmospheric impact of a series of huge volume repeated long term degassing events requires further investigation in conjunction with appropriate climate models

a long marine history of carbon cycle modulation by orbital climatic changes pacing of the marine carbon cycle by orbital forcing during the pliocene and pleistocene ice ages past 2 5 million years myr is well known as older deep sea sediment records are being studied at greater temporal resolution it is becoming clear that similar fluctuations in the marine carbon system have occurred throughout the late mesozoic and tertiary despite the absence of large continental ice sheets over much of this time variations in both the organic and the calcium carbonate components of the marine carbon system seem to have varied cyclically in response to climate forcing and carbon and carbonate time series appear to accurately characterize the frequency spectrum of ancient climatic change for the past 35 myr much of the variance in carbonate content carries the polar signal of obliquity 41 000 years 41 kyr forcing over the past 125 myr there is evidence from marine sediments of the continued role of precessional 21 kyr climatic cycles repeat patterns of sedimentation at about 100 400 and 2 400 kyr the modulation periods of precession persistently enter into marine carbon cycle records as well these patterns suggest a nonlinear response of climate and or the sedimentation of organic carbon and carbonates to precessional orbital perturbations nonlinear responses of the carbon system may help to amplify relatively weak orbital insolation anomalies into more significant climatic perturbations through positive feedback effects nonlinearities in the carbon cycle may have transformed orbital climatic cycles into long wavelength features on time scales comparable to the residence times of carbon and nutrient elements in the ocean

multiple early eocene hyperthermals their sedimentary expression on the new zealand continental margin and in the deep sea the paleocene eocene thermal maximum petm ca 55 5 ma was a geologically brief interval characterized by massive influx of isotopically light carbon extreme changes in global climate and profound variations in earth system processes an outstanding issue is whether it was an isolated event or the most prominent example of a recurring phenomenon recent studies of condensed deep sea sections support the latter but this finding remains uncertain here we present and discuss lithologic and carbon isotope records across two lower eocene outcrops on south island new zealand the petm manifests as a marl rich horizon with a significant negative carbon isotope excursion cie above in sediment deposited between 54 and 53 ma are four horizons with similar though less pronounced expressions marl beds of all five horizons represent increased terrigenous sedimentation presumably linked to an accelerated hydrological cycle five corresponding clay rich horizons and cies are found in deep sea records although the lithologic variations represent carbonate dissolution rather than siliciclastic dilution the presence of five intervals with similar systemic responses in different environments suggests a mechanism that repeatedly injected large masses of 13 c depleted carbon during the early eocene

modeling seafloor spreading rates through time a steady state model of crust production and destruction for the past 180 m y was proposed by b parsons and advocated by d rowley such a model has serious implications for models of secular variations in e g global sea level global climate and seawater chemistry this paper presents an analysis of the steady state model and then offers alternative extensions of that model that allow for non steady state production of ocean crust with time results suggest that the observed linear decrease in area versus age of ocean floor does not force a steady state view of seafloor spreading

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

the dan c2 hyperthermal event at gubbio italy global implications environmental effects and cause s abstract the dan c2 event is an early danian transient 100 kyr hyperthermal episode centered at 65 2 ma which records shifts in carbon reservoirs and ocean warming in the northwestern and southeastern sectors of the atlantic ocean here we present and discuss high resolution biochronostratigraphic and magnetic susceptibility data and geochemical records from the western tethyan contessa highway section gubbio italy which provide the first direct evidence of the dan c2 event beyond the atlantic ocean and point to the supra regional possibly global significance thereof at contessa highway the dan c2 event exhibits stressed ecological responses among calcareous nannoplankton and foraminifera which highlight marked environmental perturbation affecting the geobiosphere and resulting in enhanced eutrophication of the sea surface waters and carbonate dissolution as well as lowered oxygen content along the water column and at the sea bottom as for other early paleogene hyperthermal events the cause of the dan c2 event might likely to be found in changes potentially astronomically paced in the distribution of carbon within surface biosphere reservoirs however the role played by the concurrent third and last phase of deccan volcanism with its huge release of greenhouse gases into the atmosphere would be also taken into account in addition here we provide first evidence of a further short lived 38 kyr hyperthermal event not known up to now and that we term the lower c29n event

an integrated stratigraphic record from the paleocene of the chijiang basin jiangxi province china implications for mammalian turnover and asian block rotations new paleomagnetic and isotopic results from a similar to 1000 meter thick paleocene stratigraphic section in the chijiang basin of china s jiangxi province provide chromostratigraphic constraints on the shanghuan nongshanian asian land mammal age boundary and allow for a more accurate determination of an early paleogene paleomagnetic pole for the south china block paleomagnetic analysis of 121 sites 326 samples reveals that the shanghuan nongshanian boundary lies close to a normal to reverse polarity change stable carbon isotope analysis of dispersed organic matter and paleosol carbonates indicate a secular increase of similar to 1 5 superimposed on higher frequency variations correlation of this magnetochemostratigraphic pattern to the global timescale suggests that the polarity reversal near the shanghuan nongshanian boundary likely represents the chron c27n c26r transition the torrejonian tiffanian north american land mammal age boundary is closely correlated to this same polarity transition indicating nearly synchronous global mammalian turnover at this time because both land mammal age boundaries are thought to record turnover of mostly endemic taxa it is unlikely that the synchroneity of faunal change is due to intercontinental dispersal as documented for other early paleogene faunal transitions e g paleocene eocene boundary instead these mammalian faunal transitions may represent independent ecological or evolutionary responses to environmental changes that have been interpreted from marine records at this time e g top chron 27n event these new paleomagnetic results from the chijiang basin are also used to augment other published data and to calculate a paleocene paleomagnetic pole for the south china block the new pole shows no significant vertical axis rotation compared to the paleocene reference pole for eurasia indicating that much of the clockwise rotation that has been documented for the south china block from cretaceous deposits cannot be the result of extrusion tectonics associated with the early paleogene india asia collision observed cretaceous rotations of the south china block may be the result of late cretaceous early paleocene rifting in the backarc of the kula pacific subduction zone c 2008 elsevier b v all rights reserved

high resolution calcareous nannofossil biostratigraphy and paleoecology across the latest danian event lde in central eastern desert egypt abstract a detailed study of the calcareous nannofossil assemblages of latest danian to early selandian age from wadi qena the qreiya 1 qreiya 2 and araas sections in the central eastern desert and the gebel duwi section at the red sea coast has been carried out to understand the local phytoplankton paleocommunities for the first time in egypt four calcareous nannofossil zones ntp6 ntp7 ntp8 ntp9 and five subzones ntp7a ntp7b ntp8a ntp8b and ntp8c were distinguished subdividing the standard np4 and np5 zones the calcareous nannofossil zones were correlated with nannofossil zonations from the tethyan region e g tunisia and the zumaia section the gssp for the danian selandian boundary the calcareous nannofossil assemblages are moderately to well preserved the event beds are characterized by a dark brown shaley marl bed rich in organic carbon and coprolites three main assemblages are distinguished a pre event assemblage a transitional assemblage and a post event assemblage the paleoenvironments vary from cool eutrophic water below and above the event to warm oligotrophic conditions during the event the result of this study concludes that the latest danian event lde may represent an early paleocene hyperthermal

climate response to orbital forcing across the oligocene miocene boundary spectral analyses of an uninterrupted 5 5 million year my long chronology of late oligocene early miocene climate and ocean carbon chemistry from two deep sea cores recovered in the western equatorial atlantic reveal variance concentrated at all milankovitch frequencies exceptional spectral power in climate is recorded at the 406 thousand year ky period eccentricity band over a 3 4 million year period 20 to 23 4 my ago ma as well as in the 125 and 95 ky bands over a 1 3 million year period 21 7 to 23 0 ma of suspected low greenhouse gas levels moreover a major transient glaciation at the epoch boundary approximately 23 ma mi 1 corresponds with a rare orbital congruence involving obliquity and eccentricity the anomaly which consists of low amplitude variance in obliquity a node and a minimum in eccentricity results in an extended period approximately 200 ky of low seasonality orbits favorable to ice sheet expansion on antarctica

high resolution intra and interbasinal correlation of the danian selandian transition early paleocene the bjala section bulgaria and the selandian gssp at zumaia spain abstract the danian selandian d s boundary has been identified for the first time in the black sea coast at bjala bulgaria based on a new integrated bio magneto and cyclostratigraphic study several correlation criteria as established for the basal selandian gssp from zumaia basque basin are evaluated noteworthy is the almost complete lack of calcareous nannoplankton species braarudosphaera bigelowi in the bulgarian sections a sharp decrease of which was indicated as suitable criteria for defining the d s boundary as it occurred both at zumaia and in the classical locations of the north sea basin conversely the second evolutionary radiation of the calcareous nannofossil genus fasciculithus together with the occurrence of fasciculithus tympaniformis that define the np4 np5 zonal boundary seem to be reliable criteria to approximate the d s boundary in detail however the best approach is to integrate biostratigraphic data within a magnetostratigraphic and or cyclostratigraphic framework refinements on the placement of chron c27n at zumaia and robust bed by bed correlation between several basque sections and bjala indicates that the d s boundary is located 30 precession cycles 630 ky above c27n in addition to the precession related marl limestone couplets and 100 ky eccentricity bundles recognized in the studied sections expression of the stable 405 ky long eccentricity allows direct tuning to the astronomical solutions a correlation of the land based sections with previously tuned data from odp site1262 from the southern atlantic is challenged our choice is consistent with original tuning at zumaia but shifts one 100 ky cycle older previous tuning from site 1262 along the interval above c27n under the preferred tuning scheme the d s boundary can be given an age of 61 641 0 040 ma on the la04 orbital solution

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

stable δ13c δ18o and strontium isotopes through the paleocene at gebel aweina eastern tethyan region abstract stable 13 c 18 o and strontium 87 sr 86 sr isotopic records have been established through the paleocene section at gebel aweina in the eastern desert egypt the section has been formed in a shelf upper bathyal environment and spans the interval from planktonic foraminiferal zones p1d to p6a or p6b integrated evaluation of isotopic results and scanning electron microscope observations suggest that strontium and whole rock 13 c records reflect primarily original isotopic trends whereas 18 o and foraminiferal 13 c values have been severely affected by diagenesis the whole rock 13 c record exhibits a continuous increase of 4 from the early paleocene to middle late paleocene the increase is followed by a stepwise 13 c decrease of the same magnitude through the late late paleocene and onwards the gross trends of this 13 c record have earlier been registered in many coeval deep sea sections but there are also some significant disparities at aweina for example the paleocene carbon isotopic changes have a higher amplitude in the deep sea the mid to late paleocene 13 c increase has been interpreted to reflect high biological productivity and or changes in the global carbon mass balance the 13 c decrease in the upper part of the aweina section can be identified as the paleocene eocene transitional long term 10 3 kyr negative 13 c shift which may reflect a major reorganisation in global oceanic circulation patterns the well known latest paleocene deep sea benthic foraminiferal extinction event has been found in the upper part of the aweina section and coincides with a distinct and rapid 13 c decrease of 1 5 the benthic extinction event and the associated 13 c anomaly thus represent important stratigraphic markers also in more shallow environments the gebel aweina 13 c record shows considerably lower values compared to the global 13 c record during early and early late paleocene and in the latest paleocene in the early late paleocene foraminiferal zones p3a to the base of p4 the aweina 13 c values increase rapidly by 1 5 and converge with the global record thereafter the two records covary up to the benthic extinction event after which they diverge the convergence between the records may reflect sea level rise and more open water mass exchange between the eastern tethys and the world ocean the similarity of pilot 13 c records from greece and tunisia with the aweina record support this interpretation diagenetic processes however cannot be ruled out and further studies are required to determine the significance of the 13 c depletions in the eastern tethyan sediments the 87 sr 86 sr ratios through the paleocene at gebel aweina are remarkably invariable close to a value of 0 7077 this is the same trend that has been reported in some earlier detailed studies conducted on well preserved calcitic material from the paleocene indicating original sr isotopic signatures at gebel aweina the homogeneity of sr isotopic ratios throughout the paleocene contrasts with the prominent changes observed in the carbon isotope record indicating a decoupling of the mechanisms regulating the mass fluxes of these elements the invariable sr isotopic ratios suggest stable conditions as regards to relative changes in mass fluxes of riverine and or hydrothermal sr during the paleocene

paleosol barometer indicates extreme fluctuations in atmospheric co2 across the cretaceous tertiary boundary we present an atmospheric p co 2 p is partial pressure curve showing extreme fluctuations for the interval between ca 77 and 63 ma in southern alberta canada using a paleosol barometer paleosol carbonate nodules micrite were collected from 40 bk horizons among 6 stratigraphic sections for stable carbon isotope analysis based on results from the study area declining atmospheric p co 2 from 1200 ppmv v is volume in the campanian to 780 ppmv in the maastrichtian correlates with late cretaceous climate cooling and falling sea level as documented in global records the remarkable rise in atmospheric p co 2 near 65 5 ma 1440 ppmv correlates with volcanic activity associated with the deccan traps rising sea level and warmer global climates the decline in atmospheric p co 2 760 ppmv at the cretaceous tertiary boundary and subsequent sharp rise into the danian 1000 ppmv occurred during static terrestrial temperatures and sea level this work provides compelling evidence that atmospheric p co 2 curves modeled for the phanerozoic do not offer the resolution needed to understand environmental conditions during catastrophic events in earth9s history

pelagic evolution and environmental recovery after the cretaceous paleogene mass extinction the evolutionary recovery of planktic foraminifera from the cretaceous paleogene mass extinction was closely linked to recovery of the marine carbon system both the evolutionary recovery and the biogeochemical recovery occurred in two stages the second stage of evolutionary radiation peaked nearly four million years after the extinction immediately after the abrupt final recovery of the organic flux to deep waters the timing of these events suggests that the final postextinction recovery of planktic foraminiferal diversity was directly contingent on the final recovery of the marine carbon cycle this second radiation was defined by the diversification of tropical photosymbiotic forms that dominated low and mid latitude assemblages long into the eocene we hypothesize that this diversification was a result of the reappearance of oligotrophic oceans as the organic flux from the surface ocean to deep water fully recovered from the mass extinction

coal quality controls of the danville coal in indiana illinois basin central usa abstract the danville coal member dugger formation upper desmoinesian pennsylvanian is a significant economic coal resource in the illinois basin central usa deposition of the danville coal peat was in coastal environments varying distances from the coastline and in turn variable influences from saline waters the purpose of this study is to examine the coal quality and petrography of the danville coal and to discuss their relationship with depositional environment as it relates to the final coal product a medium sulfur 1 0 1 5 wt danville coal reserve area northern indiana coalfield was compared to a low sulfur 3 m of finer grained clastic sediments atop the danville the sulfur and trace elements contents are significantly lower

a high resolution marine 187os 188os record for the late maastrichtian distinguishing the chemical fingerprints of deccan volcanism and the kp impact event abstract a composite late maastrichtian 65 5 to 68 5 ma marine osmium os isotope record based on samples from the southern ocean odp site 690 the tropical pacific ocean dsdp site 577 the south atlantic dsdp site 525 and the paleo tethys ocean demonstrates that subaerially exposed pelagic carbonates can record seawater os isotope variations with a fidelity comparable to sediments recovered from the seafloor new results provide robust evidence of a 20 decline in seawater 187os 188os over a period of about 200 kyr early in magnetochron c29r well below the cretaceous paleogene boundary kpb confirming previously reported low resolution data from the south atlantic ocean new results also confirm a second more rapid decline in 187os 188os associated with the kpb that is accompanied by a significant increase in os concentrations complementary platinum pt and iridium ir concentration data indicate that the length scale of diagenetic remobilization of platinum group elements from the kpb is less than 1 m and does not obscure the pre kpb decline in 187os 188os increases in bulk sediment ir concentrations and decreases in bulk carbonate content that coincide with the os isotope shift suggest that carbonate burial flux may have been lower during the initial decline in 187os 188os we speculate that diminished carbonate burial rate may have been the result of ocean acidification caused by deccan volcanism

foraminiferal and δ13c isotopic event stratigraphy across the danian selandian transition at zumaya northern spain chronostratigraphic implications unconformity characterized by a ma jor lithological shift from greyish white oxic limestone chalk of the danskekalk fm upper danian to suboxic glauconitic green sand of the lellinge greensand fm lower selan dian overlain by grey marl and clay of the kerteminde marl fm middle selandian this unconformity was correlated with the sequence bound ary between cycles ta 1 3 and ta 1 4 abstract the zumaya section northern spain is a suitable candidate to define the global stratotype section and point for the base of the selandian stage palaeocene because of its excellent accessibility exposure and stratigraphic continuity uncertain ties exist however with regard to the stratigraphic horizon where to place the danian selandian d s boundary five potential stratigraphic horizons hds1 to hds5 to define the d s boundary have been identified at zumaya based on integrated stratigraphic studies that include quantitative plank tic and benthic foraminiferal results as well as d 13 c isotopic and lithological data two of these horizons hds2 and hds4 placed in zone c26r appear to have particularly good potential for serving as the d s boundary marker because they may represent significant global palaeoceanographic palaeoclimatic and eustatic events

early cenozoic benthic foraminiferal isotopes species reliability and interspecies correction factors 1 oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions with those of benthic foraminifera providing information on the deep oceans reconstructions are complicatedby interspecies isotopic offsets that result from microhabitat preferences carbonate precipitation in isotopically distinct environments and vital effects species specific metabolic variation in isotopic fractionation we provide correction factors for early cenozoic benthic foraminifera commonly used for isotopic measurements cibicidoides spp nuttallides truempyi oridorsalis spp stensioina beccariiformis hanzawaia ammophila and bulimina spp showing that most yield reliable isotopic proxies of environmental change the statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies interspecies isotopic offsets appear to have changed through the cenozoic either 1 as a result of evolutionary changes or 2 as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies regardless of the reason the assumption that isotopic offsets have remained constant through the cenozoic has introduced an 1 2 c uncertainty into deep sea paleotemperature calculations in addition we compare multiple species isotopic data from a western north atlantic section that includes the paleocene eocene thermal maximum to determine the most reliable isotopic indicator for this event we propose that oridorsalis spp was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time it may be the best recorder at other locations and for other extreme events also

ocean overturning since the late cretaceous inferences from a new benthic foraminiferal isotope compilation 1 benthic foraminiferal oxygen isotopic d 18 o and carbon isotopic d 13 c trends constructed from compilations of data series from multiple ocean sites provide one of the primary means of reconstructing changes in the ocean interior these records are also widely used as a general climate indicator for comparison with local and more specific marine and terrestrial climate proxy records we present new benthic foraminiferal d 18 o and d 13 c compilations for individual ocean basins that provide a robust estimate of benthic foraminiferal stable isotopic variations to 80ma andtentatively to 110ma first order variations ininterbasinal isotopicgradients delineate transitions from interior ocean heterogeneity during the late cretaceous 65 ma to early paleogene 35 65 ma homogeneity and a return to heterogeneity in the late paleogene early neogene 35 0 ma we propose that these transitions reflect alterations in a first order characteristic of ocean circulation the ability of winds to make water in the deep ocean circulate we document the initiation of large interbasinal d 18 o gradients in the early oligocene and link the variations in interbasinal d 18 o gradients from the middle eocene to oligocene with the increasing influence of wind driven mixing due to the gradual tectonic opening of southern ocean passages and initiation and strengthening of the antarctic circumpolar current the role of wind driven upwelling possibly associated with a tethyan circumequatorial current in controlling late cretaceous interior ocean heterogeneity should be the subject of further research

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

orbitally paced climate evolution during the middle miocene monterey carbon isotope excursion one of the most enigmatic features of cenozoic long term climate evolution is the long lasting positive carbon isotope excursion or monterey excursion which started during a period of global warmth after 16 9 ma and ended at similar to 13 5 ma approximately 400 kyr after major expansion of the antarctic ice sheet we present high resolution 1 9 kyr astronomically tuned climate proxy records in two complete sedimentary successions from the northwestern and southeastern pacific odp sites 1146 and 1237 which shed new light on the middle miocene carbon isotope excursion and associated climatic transition over the interval 17 1 12 7 ma we recog nize three distinct climate phases with different imprints of orbital variations into the climatic signals 1146 and 123 7 delta 18 o delta 13 c 1237 xrt fe fraction 63 pm 1 climate optimum prior to 14 7 ma characterized by minimum ice volume and prominent 100 and 400 kyr variability 2 long term cooling from 14 7 to 13 9 ma principally driven by obliquity and culminating with rapid cryosphere expansion and global cooling at the onset of the last and most pronounced delta 13 c increase 3 icehouse mode after 13 9 ma with distinct 100 kyr variability and improved ventilation of the deep pacific the monterey carbon isotope excursion 16 9 13 5 ma consists overall of nine 400 kyr cycles which show high coherence with the long eccentricity period superposed on these low frequency oscillations are high frequency variations 100 kyr which closely track the amplitude modulation of the short eccentricity period in contrast to delta 13 c the delta 18 o signal additionally shows significant power in the 41 kyr band and the 1 2 myr amplitude modulation of the obliquity cycle is clearly imprinted in the 1146 delta 18 o signal our results suggest that eccentricity was a prime pacemaker of middle miocene climate evolution through the modulation of long term carbon budgets and that obliquity paced changes in high latitude seasonality favored the transition into the icehouse climate c 2007 elsevier b v all rights reserved

release of methane from a volcanic basin as a mechanism for initial eocene global warming a 200 000 yr interval of extreme global warming marked the start of the eocene epoch about 55 million years ago negative carbon and oxygen isotope excursions in marine and terrestrial sediments show that this event was linked to a massive and rapid approximately 10 000 yr input of isotopically depleted carbon it has been suggested previously that extensive melting of gas hydrates buried in marine sediments may represent the carbon source and has caused the global climate change large scale hydrate melting however requires a hitherto unknown triggering mechanism here we present evidence for the presence of thousands of hydrothermal vent complexes identified on seismic reflection profiles from the voring and more basins in the norwegian sea we propose that intrusion of voluminous mantle derived melts in carbon rich sedimentary strata in the northeast atlantic may have caused an explosive release of methane transported to the ocean or atmosphere through the vent complexes close to the palaeocene eocene boundary similar volcanic and metamorphic processes may explain climate events associated with other large igneous provinces such as the siberian traps approximately 250 million years ago and the karoo igneous province approximately 183 million years ago