a cenozoic record of the equatorial pacific carbonate compensation depth atmospheric carbon dioxide concentrations and climate are regulated on geological timescales by the balance between carbon input from volcanic and metamorphic outgassing and its removal by weathering feedbacks these feedbacks involve the erosion of silicate rocks and organic carbon bearing rocks the integrated effect of these processes is reflected in the calcium carbonate compensation depth which is the oceanic depth at which calcium carbonate is dissolved here we present a carbonate accumulation record that covers the past 53 million years from a depth transect in the equatorial pacific ocean the carbonate compensation depth tracks long term ocean cooling deepening from 3 0 3 5 kilometres during the early cenozoic approximately 55 million years ago to 4 6 kilometres at present consistent with an overall cenozoic increase in weathering we find large superimposed fluctuations in carbonate compensation depth during the middle and late eocene using earth system models we identify changes in weathering and the mode of organic carbon delivery as two key processes to explain these large scale eocene fluctuations of the carbonate compensation depth

rapid stepwise onset of antarctic glaciation and deeper calcite compensation in the pacific ocean the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the calcite compensation depth at present this depth is 4 500 m with some variation between and within ocean basins the calcite compensation depth is linked to ocean acidity which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate1 geological records of changes in the calcite compensation depth show a prominent deepening of more than 1 km near the eocene oligocene boundary 34 million years ago 2 when significant permanent ice sheets first appeared on antarctica3 4 5 6 but the relationship between these two events is poorly understood here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical pacific ocean that cover the eocene oligocene boundary we find that the deepening of the calcite compensation depth was more rapid than previously documented and occurred in two jumps of about 40 000 years each synchronous with the stepwise onset of antarctic ice sheet growth the glaciation was initiated after climatic preconditioning7 by an interval when the earth s orbit of the sun favoured cool summers the changes in oxygen isotope composition across the eocene oligocene boundary are too large to be explained by antarctic ice sheet growth alone and must therefore also indicate contemporaneous global cooling and or northern hemisphere glaciation

erosional troughs in deep sea carbonates and their relationship to basement structure abstract a detailed survey of a small area in the eastern equatorial pacific with the marine physical laboratory s deep tow instrument package reveals erosionally excavated troughs in an area of relatively rapid accumulation of carbonate the troughs lie on top of a basement high implying a relationship between the troughs and the basement feature differential accumulation and compaction may explain the origin of the troughs sediment deposited around the basement high preferentially accumulates on gentle slopes and in troughs this results in a thick sequence of sediment on the flanks of the basement high and a thin sequence above on top of the hill unstable sediment masses and differential compaction generate a tensile stress field above the peak of the basement high which causes slumping and faulting the steep slopes generated by faulting and slumping may then serve to intensify tidal currents or act as spillways and locally generate increased turbulence this increased turbulence results in local erosion by dissolution a trough will form above a basement high however only when a combination of 1 basement steepness 2 high sedimentation rate 3 sediment thickness and 4 sediment erodibility are present

strain factorization by identical finite increments and its use abstract progressive deformation of layered rocks up to their present finite strain and bedding attitudes is simulated by an identical increment path model a deformation matrix connecting the initial and deformed states is formulated with the conceptual help of a hypothetical three step deformation path two sequential non coaxial rigid body rotations bring an original horizontal bed to a pre strain attitude a pure shear follows the rotations thus the deformation matrix is calculated by premultiplying the matrices representing the three stages of deformation sixteen identical tectonic deformation increments are then obtained by four times sequentially extracting the square root of that deformation matrix the method has been applied to the campbell block a late jurassic fault bounded turbidite sliver in the northern sierra nevada california the block was deformed into a train of folds during the nevadan orogeny fourteen oriented samples were collected for march strain measurements based on the strains and bedding attitudes the block was divided into 11 deformation bands of three types by applying the proposed model to the campbell block it was found that the deformation style of the block consists of a non coaxial deformation path the regional strain is accommodated among the several deformation bands by strain partitioning the collective deformation indicated by this model is transpressional

latest eocene early oligocene climate change and southern ocean fertility inferences from sediment accumulation and stable isotope data abstract the earliest oligocene 33 5 ma is marked by a major step in the long term transition from an ice free to glaciated world the transition characterized by both cooling and ice sheet growth triggered a transient but extreme glacial period designated oi 1 high resolution isotope records suggest that oi 1 lasted for roughly 400 000 yr the duration of magnetochron 13n before partially abating and that it was accompanied by an ocean wide carbon isotope anomaly of 0 75 one hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate induced intensification of wind stress and upwelling particularly in the southern ocean to understand how this climatic event affected export production in the southern ocean biogenic silica opal and carbonate accumulation rates were computed for the sub polar indian ocean using deep sea cores from odp site 744 kerguelen plateau our findings suggest that net productivity in this region increased by several fold in response to the oi 1 glaciation in addition calcareous primary producers dominant in the late eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the southern ocean we attribute these changes to intensification of atmospheric oceanic circulation brought about by high latitude cooling and the appearance of a full scale continental ice sheet on east antarctica higher terrigenous sediment accumulation rates support the idea that wind induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro nutrients e g iron rich dust particles we speculate that the rapid changes in biogenic sediment accumulation in the southern ocean and other upwelling dominated regions contributed to the ocean wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon the changes in burial rates in turn may have produced a positive feedback on climate by briefly drawing down atmospheric pco2

cooling and ice growth across the eocene oligocene transition the eocene oligocene e o climate transition ca 34 ma marks a period of antarctic ice growth and a major step from early cenozoic greenhouse conditions toward today s glaciated climate state the transition is represented by an increase in deep sea benthic foraminiferal oxygen isotope 18o values occurring in two main steps that reflect the temperature and 18o of seawater existing benthic mg ca paleotemperature records do not display a cooling across the transition possibly reflecting a saturation state effect on benthic foraminiferal mg ca ratios at deep water sites here we present data from exceptionally well preserved foraminifera deposited well above the calcite compensation depth that provide the first proxy evidence for an 2 5 c ocean cooling associated with the ice growth this permits interpretation of e o 18o records without invoking northern hemisphere continental scale ice

hydrothermal pits in the biogenic sediments of the equatorial pacific ocean 1 a recent expedition to the equatorial pacific surveyed over 60 000 km2 of seafloor using swath map imaging and high resolution seismic profiling this survey revealed the common occurrence of large pits in the biogenic sediments that are usually associated with basement highs the pits range in size up to a few kilometers across and are on the order of 50 m 100 m deep they were found on seafloor ranging in age from 15 ma to 55 ma with overlying sediment cover up to 500 m thick we link their origin with hydrothermal discharge through conduits created by differential compaction and fracturing over basement highs and by basement faulting that penetrates the overlying sediments although carbonate dissolution is likely to be associated with the formation of the pits their occurrence shows no consistent relationship with the present calcite compensation depth ccd

rapid cenozoic glaciation of antarctica induced by declining atmospheric co2 the sudden widespread glaciation of antarctica and the associated shift towards colder temperatures at the eocene oligocene boundary 34 million years ago refs 1 4 is one of the most fundamental reorganizations of global climate known in the geologic record the glaciation of antarctica has hitherto been thought to result from the tectonic opening of southern ocean gateways which enabled the formation of the antarctic circumpolar current and the subsequent thermal isolation of the antarctic continent5 here we simulate the glacial inception and early growth of the east antarctic ice sheet using a general circulation model with coupled components for atmosphere ocean ice sheet and sediment and which incorporates palaeogeography greenhouse gas changing orbital parameters and varying ocean heat transport in our model declining cenozoic co2 first leads to the formation of small highly dynamic ice caps on high antarctic plateaux at a later time a co2 threshold is crossed initiating ice sheet height mass balance feedbacks that cause the ice caps to expand rapidly with large orbital variations eventually coalescing into a continental scale east antarctic ice sheet according to our simulation the opening of southern ocean gateways plays a secondary role in this transition relative to co2 concentration

the shaping of continental slopes by internal tides the angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins 2 to 4 degrees intensification of near bottom water velocities and bottom shear stresses caused by reflection of semi diurnal internal tides affects sedimentation patterns and bottom gradients as indicated by recent studies of continental slopes off northern california and new jersey estimates of bottom shear velocities caused by semi diurnal internal tides are high enough to inhibit deposition of fine grained sediment onto the slopes

from tides to mixing along the hawaiian ridge the cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing we investigated this cascade along the hawaiian ridge using observations and numerical models a divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models large internal tidal waves with peak to peak amplitudes of up to 300 meters occur on the ridge internal wave energy is enhanced and turbulent dissipation in the region near the ridge is 10 times larger than open ocean values given these major elements in the tides to turbulence cascade an energy budget approaches closure

eocene biogenic silica accumulation rates at the pacific equatorial divergence zone 2 the eocene biosiliceous oozes of the tropical pacific are an easily recognizable sediment type having a reddish brown color and sugary texture these sediments are dominated by radiolarian tests with traces of terrigenous debris hydrothermal oxides a few diatoms and little if any carbonate the paucity of carbonate is a result of the very shallow pacific calcite compensation depth ccd of the eocene 3300 m rea and lyle 2005 and references therein the dominance of radiolarian tests over those of diatoms is an enigma in that diatoms usually dominate siliceous rich sediments of the oligocene and neogene the opal rich character of these eocene sediments is commonly associated with the development of cherts within the sections 3 these unusual characteristics of eocene radiolarian oozes have prompted some authors to puzzle over how so much silica could have been delivered to the sea floor during

palaeomagnetism of granitic intrusives from the precambrian basement under eastern kansas orienting drill cores using secondary magnetization components summary the precambrian basement under east central kansas was drilled at two circular aeromagnetic positives one at osawattamie and one at big springs the core retrieved from these sites is a coarse to medium grained granite which has been dated by u pb to be 1350 ma old the palaeomagnetism of these azimuthally unoriented cores was studied to see if a technique which uses low coercivity low temperature magnetization components to orient the cores would allow an independent confirmation of the core s mid proterozoic age orthogonal projection plots of the alternating field af and thermal demagnetization data show that the magnetization of these cores is relatively simple having only two components a low temperature low coercivity magnetization with steep positive inclinations and a shallow negative inclination characteristic magnetization for the osawattamie core or a positive moderate inclination characteristic magnetization for the big springs core if the declination of the low temperature low coercivity component is aligned parallel to the present field declination the characteristic directions may be azimuthally oriented this allows the calculation of palaeomagnetic poles for the big springs core lat 4 5 s long 29 9 e and the osawattamie core lat 20 2 n long 39 3 e which are consistent with irving s apparent polar wander path for laurentia at about 1300 1400 ma comparison of anhysteretic remanent magnetization arm viscous remanent magnetization vrm and isothermal remanent magnetization af demagnetization curves with a natural remanent magnetization nrm demagnetization curve suggests that the osawattamie core probably acquired a piezoremanent magnetization prm parallel to the core axis during drilling

radiolarian faunal turnover and paleoceanographic change around eocene oligocene boundary in the central equatorial pacific odp leg 199 holes 1218a 1219a and 1220a continuous eocene through oligocene sedimentary sedimentary sections were obtained at holes 1218a 1219a and 1220a drilled during leg 199 of the ocean drilling program in the central equatorial pacific quantitative analysis of radiolarian assemblages between the upper eocene through lower oligocene sedimentary successions revealed that major faunal changes of radiolarians occurred in the late eocene 35 5 35 7 ma subchron c16n1 around the eocene oligocene boundary 33 7 33 8 ma upper subchron c13r and in the early oligocene 30 9 31 3 ma uppermost subchron c12r the faunal change in the late eocene is characterized by a stepwise decrease of tropical eocene species and an increase in cosmopolitan probably cool water tolerant radiolarians however without a significant change in species diversity and radiolarian accumulation rates the stratigraphic level of this late eocene turnover came after the late eocene impact event and may have been more related to global cooling and associated oceanographic changes than to asteroid impact the turnover around the eocene oligocene boundary corresponding to the oi 1 event is the most critical during the eocene oligocene transition many biotic events such as a sudden drop of species diversity an increase in the cosmopolitan radiolarian group a large number of species turnovers and a drop in radiolarian accumulation rates occurred at or just above this level together these indicators suggest a major restructuring of radiolarian assemblages from the high diversity eocene fauna to a low diversity oligocene one the third turnover event within early oligocene is represented by a replacement of dominant species with a sudden decrease in radiolarian accumulation rates however this oligocene turnover is not consistent with other major 18o isotope events such as oi 1b and oi 2

sediment mixing in the tropical pacific and radiolarian stratigraphy 1 the reworking of older radiolarian microfossils into near surface sediments of the tropical pacific has long been the source of confusion for the development of radiolarian stratigraphy and of puzzlement over the mechanism s that could effect such pervasive reworking widespread dissolution pits in the sediments of the tropical pacific are believed to be associated with hydrothermal circulation cells in the older oceanic crust and are here linked to processes which expose older sections and inject older non carbonate material into near bottom waters discharging waters of these circulation cells tend to dissolve carbonate in near surface sediments thus only the non carbonate material including radiolarians is preserved and reworked into younger sediments results from the study of two sites in the tropical pacific indicate that reworked older stratigraphically important radiolarians are less than 2 of the total radiolarian assemblage this constitutes a minimum estimate of the amount of reworked non carbonate material in the younger sediments the oldest reworked radiolarians are no more than 10 m y younger than the underlying basement and radiolarians from the entire older section above that level can be found in the reworked material a time series of the flux of reworked material at one site is not constant but instead has varied by a factor of 3 to 4 over the past 2 5 m y during times when the flux of reworked material is particularly low the proportion of older more robust radiolarians is larger

extinction and environmental change across the eocene oligocene boundary in tanzania the eocene oligocene transition between ca 34 and 33 5 ma is the most profound episode of lasting global change to have occurred since the end of the cretaceous diverse geological evidence from around the world indicates cooling ice growth sea level fall and accelerated extinction at this time turnover in the oceanic plankton included the extinction of the foraminifer family hantkeninidae which marks the eocene oligocene boundary in its type section another prominent extinction affected larger foraminifera which resulted in the loss of some of the world s most abundant and widespread shallow water carbonate secreting organisms however problems of correlation have made it difficult to relate these events to each other and to the global climate transition as widely recorded in oxygen and carbon isotope records from deep sea cores here we report new paleontological and geochemical data from hemipelagic sediment cores on the african margin of the indian ocean tanzania drilling project sites 11 12 and 17 the eocene oligocene boundary is located between two principal steps in the stable isotope records the extinction of shallow water carbonate producers coincided with an extended phase of ecological disruption in the plankton and preceded maximum glacial conditions in the early oligocene by 200 k y

major shifts in calcareous phytoplankton assemblages through the eocene oligocene transition of tanzania and their implications for low latitude primary production a high resolution record of exceptionally well preserved calcareous nannofossil assemblages from tanzania is marked by two key transitions closely related to the climatic events of the eocene oligocene transition eot the first transition at similar to 34 0 ma precedes the first positive shift in delta o 18 and coincides with a distinct interval of very low nannofossil abundance and a cooling in sea surface temperatures sst the second at similar to 33 63 ma is immediately above the eocene oligocene boundary eob and is associated with a significant drop in nannofossil diversity both transitions involve significant reductions in the abundance of holococcoliths and other oligotrophic taxa these changes in calcareous phytoplankton assemblages indicate 1 a widespread and significant perturbation to the low latitude surface ocean closely tied to the eob 2 a potential role for reduced carbonate primary production at the onset of global cooling and 3 a significant increase in nutrient availability in the low latitude surface ocean through the eot

erosion and reworking of pacific sediments near the eocene oligocene boundary 1 the eocene oligocene e o boundary interval marks one of the largest and most rapid changes in climate during the last 50 myr because of a very shallow calcium carbonate compensation depth in the eocene as well as the reworking of sediments and hiatuses in the boundary zone it has also been one of the most difficult stratigraphic boundaries to study in deep water marine sections especially in the pacific ocean recently three drill sites have recovered complete sections of the e o boundary interval in the tropical pacific a detailed study of these sections shows a series of pulses of reworked older radiolarians in the upper eocene and lowermost oligocene the two largest pulses are coincident with the two sharp steps in carbon and oxygen isotope values that bracket the e o boundary several smaller peaks in reworked material precede these two maxima it is proposed that immixing of the older radiolarian species results from erosion and redeposition possibly linked to pulses of new bottom water formation and the formation of a deep pycnocline

modeling cenozoic sedimentation in the central equatorial pacific and implications for true polar wander high productivity along the central pacific equator has left thick deposits of calcareous and siliceous ooze west of 102 w these have deposited on the pacific plate which has been drifting northwards and therefore the thickest deposits are displaced north of the equator this study attempts to simulate the sediment distribution using information from deep sea drilling project dsdp cores and models for pacific plate motion the dsdp core data are used to account for accumulation rate variations with time paleolatitude and paleodepth accounting for variable carbonate dissolution the model predicts the distribution on 35 50 ma seafloor relatively well and demonstrates that the sedimentary bulge is distorted by variable dissolution over a regional bathymetry gradient due to the northern edge of the south pacific superswell a westerly deepening of the carbonate compensation depth and sedimentary lysocline evolution are proposed which improve the model for seafloor 30 ma and older the degree of match between model and data provides a test of the amount of northward drift of the pacific plate and assuming a model for pacific hotspots motion of true polar wander tpw motion of the hotspot frame relative to the earth s spin axis assuming the duncan and clague 1985 model for pacific hotspots motion the sedimentary modeling favors tpw models which have little or no effect on the central pacific paleoequator over the past 30 ma we also explore implications of interhotspot motion and the suggestion that the bend in the hawaiian volcanic chain represents an abrupt change in pacific hotspot motion within the last 5 ma

planktonic foraminiferal turnover diversity fluctuations and geochemical signals across the eocene oligocene boundary in tanzania a major turnover in planktonic foraminifera occurred across the eocene oligocene e o boundary new drill holes through the e o boundary in southern tanzania contain extremely well preserved and diverse assemblages of planktonic foraminifera here we document a 1 2 million year record of assemblages diversity and stable isotope fluctuations through this critical interval which is often dissolved and or recrystallised in carbonate rich facies the e o boundary is marked by the abrupt extinction of all five remaining species of the family hantkeninidae and a distinct size reduction in the genus pseudohastigerina the boundary is preceded over a short stratigraphic interval by the extinction of turborotalia cerroazulensis turborotalia cocoaensis and turborotalia cunialensis quantitative analysis of planktonic foraminiferal assemblages reveals significant changes in the abundance of certain species and the composition of the assemblages we compare diversity fluctuations to the stable isotope record of pseudohastigerina naguewichiensis and use multispecies stable isotope analyses to determine the life habitats of the most important species a major shift in the evenness occurs at 33 8 ma associated with the extinction of the t cerroazulensis group suggesting acute ecological disturbance we propose that the extinction of the t cerroazulensis group at 33 8 ma was directly related to cooling of sea surface temperatures while the extinction of hantkeninidae was due to modifications in the thermal structure of the oceans and associated productivity changes after the extinctions renewed origination and diversification occurred leading to a characteristic oligocene planktonic foraminifer assemblage