middle miocene ocean climate transition high resolution oxygen and carbon isotopic records from deep sea drilling project site 588a southwest pacific high resolution stable isotopic records are presented for the epi benthic foraminifer cibicidoides the inferred shallow dwelling planktonic globigerinoides quadrilobatus and the inferred deep dwelling planktonic globoquadrina dehiscens from the middle miocene 16 12 ma of deep sea drilling project site 588a lord howe rise southwest pacific high resolution multiple species oxygen and carbon isotopic data define the timing and character of the well known middle miocene climatic oceanographic transition with a resolution comparable to quaternary records the benthic foraminiferal 18o record is marked by several large fluctuations from 16 to 14 8 ma followed by a series of rapid 50 kyr 18o increases that suggest a new state of the ocean climate system after 14 8 ma the total middle miocene benthic oxygen isotopic increase of 1 2 is largely incorporated in two steps an increase of 0 8 from 14 5 to 14 0 ma and a second increase of 0 7 from 13 45 to 12 45 ma each step is comprised of a series of marked 18o increases indicative of rapid east antarctic ice sheet growth and contemporaneous deepwater cooling a strong covariance of 0 7 between the benthic and deep dwelling planktonic species from 14 5 to 14 0 ma including a rapid increase from 14 1 to 14 05 ma suggests a 0 7 increase in the 18o composition of seawater 18osw because of east antarctic ice sheet growth comparison of the 18o record of gs quadrilobatus suggests that surface waters warmed at this site by 3 c from 14 1 to 13 6 ma carbon isotopic time series for each species generally covary throughout the early to middle miocene interval 16 12 ma confirming that 13c variations in this interval largely represent reservoir changes high resolution 13c data allow improved resolution of the latter five of six 13c maxima within the well known early to middle miocene carbon isotopic excursion the monterey carbon isotopic excursion from 17 0 to 13 5 ma this is useful for global correlation the last of these maxima ends with a 1 decrease centered from 13 9 to 13 7 ma 300 kyr after the 18o increase considered to reflect east antarctic ice growth covariance between benthic 18o and 13c from 16 to 13 8 ma suggests a sensitive relation between global carbon cycling and the ocean climate system prior to 13 8 ma episodic increases in organic carbon burial may have contributed to deep sea benthic 13c maxima and synchronous global cooling the positive relationship ended at 13 8 ma indicative of changing relations between global carbon cycling and the ocean climate system brought on by the increased stability of the east antarctic ice sheet after a major growth phase from 14 5 to 14 0 ma

oxygen isotope calibration of the onset of ice rafting and history of glaciation in the north atlantic region we report here that dsdp site 552a cored with the hydraulic piston corer on the west flank of rockall bank recovered an undisturbed sequence of alternating white deep sea carbonate oozes and dark coloured layers that are rich in glacial debris oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice rafting occurred at about 2 4 myr and was preceded by a minor pulse of ice rafting at about 2 5 myr the carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present day north atlantic deep water at least since 3 5 myr

phosphogenesis and weathering of shelf sediments from the southeastern united states implications for miocene δ13c excursions and global cooling the enormous phosphorite deposits of the southeastern united states indicate intense upwelling but contain small amounts of organic carbon the authors propose that deposition of organic rich sediment on continental shelves in the southeastern united states and elsewhere during marine transgressions in the late oligocene and early to middle miocene resulted in global positive delta sup 13 c shifts and the formation of early diagenetic phosphorite multiple reworking and supergene weathering from subaerial exposure during miocene marine regressions oxidized most of the organic carbon and resulted in the return of delta sup 13 c to its preexcursion value the estimated phosphorite content of the southeastern united states requires sufficient organic carbon burial 10 sup 15 kg carbon to support a 1 per thousand delta sup 13 c excursions sea level fluctuations organic carbon burial phosphogenic episodes and possibly global cooling during the cenozoic

successional changes of middle miocene diatom assemblages in the northwestern pacific abstract miocene diatom assemblages in four sections in japan and at dsdp site 438 off the coast of northeast japan have been examined quantitatively in order to determine floral changes through time and to compare with the quantitative results from the equatorial pacific the areal distribution of some diatom levels reveals diachronous distribution across the subarctic boundary by the effect of a climatic wedge during the interval between 14 0 and 13 3 ma the middle miocene diatom assemblages turned from warm water assemblages to cold water assemblages and the number of first and last appearances of diatom species was highest at 13 8 ma the cold water diatom denticulopsis hustedtii increased abruptly in abundance at about 13 8 ma in the middle miocene the cyclic peaks in the abundance of denticulopsis hustedtii are recognized at 12 8 and 12 0 11 8 ma suggesting a cooling in the surface water temperatures during the late middle and early late miocene the pronounced abundances in both the cold water diatom denticulopsis hustedtii and the upwelling related diatom thalassionema nitzschioides are recognized and associated with the increased vigorous oceanic circulation and the increased upwelling caused by steepening of the latitudinal temperature gradient

geochronological evidence supporting antarctic deglaciation three million years ago the response of the antarctic ice sheets to increased global temperatures is an important unresolved issue in the assessment of future climate change in particular considerable controversy exists as to whether the east antarctic ice sheet suffered extensive deglaciation during the mid pliocene epoch 3 myr ago when temperatures were only slightly warmer than today although the ice sheet is widely assumed to have existed in something like its present form for the past 14 myr ref 1 marine diatoms eroded from the antarctic interior have been found in glacial till deposits high in the transantarctic mountains2 3 and have been bio stratigraphically dated at 3 myr before present this age has been disputed4 because it implies marine deposition in the antarctic interior and hence substantial deglaciation at a time when other evidence has been marshalled for the persistence of cold polar conditions4 here we report k ar and 40ar 39 ar ages for a volcanic ash bed in diatom bearing glaciomarine strata cored in ferrar fiord east antarctica by the ciros 2 drill hole5 which confirm the age of the diatoms at 3 myr and hence also confirm the mid pliocene deglaciation

cenozoic ice volume history development of a composite oxygen isotope record to view cenozoic ice volume and ocean temperature history a composite 18 o time series was constructed for tropical shallow dwelling planktonic foraminifers and for deep water benthic foraminifers we conclude that cenozoic benthic 18 o primarily reflect considerable deep ocean temperature variation and that tropical planktonic 18 o afford the best record of cenozoic ice volume the planktonic composite indicates the presence of a significant ice budget for the past 40 m y the difference between the benthic and planktonic 18 o composites suggests that low latitude production of warm saline bottom water dominated tertiary thermohaline circulation

taxonomic evolution of neogene planktonic foraminifera and paleoceanographic relations the taxonomic evolution of neogene 24 ma to present day planktonic foraminiferal species are described using four indices rate of speciation rate of extinction rate of diversification and rate of turnover the evolution of neogene planktonic foraminifera is marked by three principal stages 1 a diversification stage 24 to 16 ma early miocene 2 an equilibrium stage 16 to 5 ma middle and late miocene and 3 a declining stage 5 ma to recent pliocene and quaternary the early miocene diversification was in response to an increase in polar to equatorial thermal gradients and related subdivision of surface water masses during the middle and late miocene the assemblages remained close to their equilibria with relatively low diversification rates the decline in diversity during the pliocene and quaternary probably resulted from adverse effects imposed by both large scale paleoceanographic fluctuations that began about 6 ma and high frequency climatic oscillations related to northern hemisphere glaciations and deglaciations that began at about 2 5 ma bursts of evolutionary activity marked by higher rates of turnover coincided with major paleoceanographic changes average evolutionary rates appear to be similar for tropical transitional and temperate assemblages although the actual numbers of extinctions and speciations are higher in tropical assemblages because of higher standing diversity contemporaneity of turnover peaks in the three climatic regimes indicates global control of paleoceanographic perturbations upon planktonic foraminiferal evolution the observed evolutionary pattern supports the stationary model of stenseth and maynard smith 1984

the petroleum potential of tertiary coals from western indonesia relationship to mire type and sequence stratigraphic setting abstract more than 500 deltaic sediments from 14 basins in western indonesia were subjected to detailed geochemical petrographic and palynological analysis the resultant data represent each of the main peat forming tectonostratigraphic episodes paleogene syn rift transgressive paleogene neogene post rift transgressive and neogene syn tectonic regressive of the indonesian tertiary the coals are hydrogen rich with average hydrogen index hi of 250 300 and atomic h c ratios of 1 0 1 3 where immature paleogene coals from syn rift transgressive systems tracts are more hydrogen rich than neogene coals from syn tectonic regressive systems tracts and upon pyrolysis yield lower gas oil ratios implying they are more oil prone pliocene coals from a strongly regressive sequence in the sumatran fore arc are very hydrogen poor with average hi of 138 indonesian coals display a systematic increase in hi with increasing rank peaking at a tmax of c 430 c suggesting that rock eval pyrolysis underestimates petroleum potential in low rank coals the increase in hi is accompanied by a decrease in s1 toc ratio and the disappearance of suberinite and resinite reflecting the assimilation of these macerals into the coal matrix with increasing diagenesis petrographic analyses reveal a very poor correlation between liptinite content and hi the term detrovitrinite index di is coined to describe the ratio of detrovitrinite total vitrinite a better relationship between hi and di suggests that vitrinite type is a more important control on petroleum potential than liptinite content the coals are classified into four sub types i iv on the basis of their pyrolysis potential and petrographic composition sub types i ii and iii are low ash coals and are likely to have been deposited in raised mires sub type i is hydrogen rich and primarily represents middle to late miocene coals deposited in a regressive megasequence sub type ii coals are hydrogen poor and occur in multiple tectonostratigraphic settings sub type iii consists of very hydrogen poor pliocene coals from the rapidly subsiding west sumatran fore arc sub type iv is hydrogen rich and consists of high ash eocene coals deposited in submerged mires in a transgressive syn rift setting a close relationship between hi and tissue preservation index tpi suggests that the degree of degradation of the peat is an important factor in determining petroleum potential highly degraded peats result in hydrogen rich coals with a higher proportion of vitrinite of detrital or allochthonous origin the degree of degradation is most likely related to the amount of time the peat spends within the zone of influence of the water table and is unlikely to be directly related to tectonostratigraphic setting

a 20 ma pollen record of east asian summer monsoon evolution from guyuan ningxia china abstract pollen analysis was conducted on the fluviolacustrine sediments from the east side of the liupan mountains a relatively monsoon sensitive region and provided for the first time a continuous evolutionary history of vegetation and climate in east china during the neogene the pollen record spanning the last 20 ma indicates that the vegetation and thus east asian summer monsoon evolution can be divided into three stages 20 13 14 25 ma 14 25 11 35 ma and 11 35 0 08 ma in spite of general dominance of steppe throughout the neogene during the period 20 13 14 25 ma the pollen assemblage was characterized by high abundance of artemisia and small amounts of temperate to subtropical deciduous broad leafed trees such as juglans carya quercus and betula suggesting that the east asian summer monsoon was generally strong the interval from 14 25 to 11 35 ma was marked by a significant decline in the east asian summer monsoon as indicated by artemisia gradually replaced by humulus and halophytic chenopodiaceae nitraria and ephedra also reached high values in this period since 11 35 ma ago percentages of halophytes dominated by chenopodiaceae and tamaricaceae maintained a high mean value of about 40 revealing a weak intensity of east asian summer monsoon the general weakening of the monsoon circulation during the neogene and the significant monsoon decline during the late middle miocene in particular might link with the global cooling trend probably through two mechanisms cooling and ice sheet expansion over the polar region caused an increase in meridional temperature gradients leading to the southward retreat of the monsoon circulation the global cooling may have also reduced the amount of water vapor held in the atmosphere and led to both additional cooling and further weakening of the east asian summer monsoon the cause for a short lived resumption during the period 1 0 0 8 ma is under investigation

minimal influence of recrystallization on middle miocene benthic foraminiferal stable isotope stratigraphy in the eastern equatorial pacific stable carbon and oxygen isotopes 13c and 18o of foraminiferal tests are amongst the most important tools in paleoceanography but the extent to which recrystallization can alter the isotopic composition of the tests is not well known here we compare three middle miocene 16 13 ma benthic foraminiferal stable isotope records from eastern equatorial pacific sites with different diagenetic histories to investigate the effect of recrystallization to test an extreme case we analyzed stable isotope compositions of benthic foraminifera from integrated ocean drilling program site u1336 for which the geochemistry of bulk carbonates and associated pore waters indicates continued diagenetic alteration in sediments 14 7 ma despite this diagenetic overprinting the amplitudes and absolute values of the analyzed u1336 stable isotopes agree well with high resolution records from better preserved sites u1337 and u1338 nearby our results suggest that although benthic foraminiferal tests of all three sites show some degree of textural changes due to recrystallization they have retained their original stable isotope signatures the good agreement of the benthic foraminiferal stable isotope records demonstrates that recrystallization occurred extremely rapidly 100 kyr after deposition this is confirmed by the preservation of orbital cyclicities in u1336 stable isotope data and 18o values being different to inorganic calcite that would precipitate from u1336 pore waters during late recrystallization the close similarity of the benthic foraminiferal stable isotope records between the sites allows the well resolved paleomagnetic results of site u1336 to be transferred to sites u1337 and u1338 improving the global geological timescale

equatorial pacific deep sea benthic foraminifera faunal changes before the middle miocene polar cooling data on the composition of benthic foraminiferal faunas at deep sea drilling project site 575 in the eastern equatorial pacific ocean were combined with benthic and planktonic carbon and oxygen isotope records and caco 3 data changes in the composition of the benthic foraminiferal faunas at site 575 predated the middle miocene period of growth of the antarctic ice cap and cooling of the deep ocean waters by about 2 m y and thus were not caused by this cooling as has been proposed the benthic faunal changes may have been caused by increased variability in corrosivity of the bottom waters possibly resulting from enhanced productivity in the surface waters

the miocene climatic optimum evidence from ectothermic vertebrates of central europe abstract data sets of central european temporal distributions of thermophilic ectothermic vertebrates channidae varanidae chamaeleonidae cordylidae tomistomidae alligatoridae giant turtles and of north alpine foreland basin nafb distributions of ectothermic vertebrates adapted to dryer habitats albanerpeton inexpectatum salamandra sansaniensis bufo cf viridis chamaeleo caroliquarti gekkonidae varanus hofmanni bransateryx sp are analysed two main migration events of thermophilic ectotherms at 20 ma and 18 ma in the lower miocene are discerned they indicate the beginning of the miocene climatic optimum in central europe 42 45 n palaeolatitude with a lower limit of the mean annual temperature mat of 17 4 c derived from the minimal mat of their extant relatives furthermore additional palaeobotanical data and records of bauxite point to a mat of 22 c this warm and humid optimum peaked at 18 16 5 ma ottnangian karpatian and is confirmed by the coexistence of all investigated thermophilic taxa the following period early badenian is characterised by probably unchanged temperatures but a seasonality in precipitation with dry periods up to six months two major seasonal phases between 16 3 and 15 7 ma earliest early badenian and between 14 7 and 14 5 ma early middle badenian transition are indicated by an immigration of dry adapted taxa from the surrounding karst plateau to the nafb it is presumed that the tectonical reorganisation of the central paratethys realm had considerable influence on this regional humidity pattern the warm period ended abruptly between 14 0 and 13 5 ma middle late badenian transition with major regional extinction events of most of the thermophilic groups in central europe and a drop of the mat of probably more than 7 c to temperatures around 14 8 15 7 c this drop can be attributed predominantly to a decrease of more than 11 c of the minimum cold months temperature this temperature decrease marked the beginning of a climatic zonation of the european continent and is also evidenced by a progressively southward disappearance of the crocodile diplocynodon from 38 45 n palaeolatitude to 30 37 n during the middle and earliest late miocene the results correlate well with palaeobotanical data from the mid latitudes of europe and north america and the deep sea temperature curve generated from oxygen isotope ratios

neogene mammalian faunal change in southern asia correlations with climatic tectonic and eustatic events the fluvial neogene siwalik formations of northern pakistan span long time intervals with only minor hiatuses and being highly fossiliferous are uniquely suited for studies of change in mammalian faunas magnetostratigraphic correlations of a critical stratigraphic section give dates for 45 middle and late miocene biostratigraphic events these mark either first appearances or extinctions in the mammal fauna and show that in the siwaliks there were major fauna turnovers at between 20 and 16 ma and at 9 5 and 7 4 ma two minor faunal events are dated at 13 2 and about 12 ma many species making their first appearance were immigrants from europe or africa and indicate when connections to those regions existed immigration and extinction were the dominant modes of faunal change in situ evolution was much less important the siwalik biostratigraphic record correlates closely to climatic oceanographic and tectonic events which probably controlled immigration into southern asia abiotic events were therefore important factors affecting evolution of the mammal communities

tertiary oxygen isotope synthesis sea level history and continental margin erosion tertiary benthic and planktonic foraminiferal oxygen isotope records are correlated to a standard geomagnetic polarity time scale making use of improved chronostratigraphic control and additional oligocene isotope data synchronous changes in both benthic and planktonic 18o values which occurred in the oligocene to miocene 36 5 2 ma are interpreted in part to represent ice growth and decay the inferred ice growth events correlate with erosion on passive continental margins as interpreted from seismic and chronostratigraphic records this association is consistent with a link between oligocene to miocene erosional events and rapid 15 m m y glacioeustatic lowerings of about 50 m high benthic foraminiferal 18o values suggest the presence of continental ice sheets during much of the oligocene to recent 36 0 ma substantially ice free conditions probably existed throughout the paleocene and eocene 66 36 ma the mechanisms and rates of sea level change apparently were different between the early and late tertiary with glacioeustatic changes restricted to the past 36 m y pre oligocene erosion on passive continental margins was caused by eustatic lowerings resulting from global spreading rate changes we apply a model which suggests that large areas of the continental shelves were subaerially exposed during such tectonoeustatic lowstands stimulating slope failure and submarine erosion the different mechanisms and rates of eustatic change may have caused contrasting erosional patterns between the early and late tertiary on passive continental margins this speculation needs to be confirmed by examination of data from several passive margins

late cenozoic glacial history of the ross embayment antarctica abstract knowledge of the cenozoic terrestrial and marine glacial history of antarctica has been developed through studies of on land surface outcrops and subsurface drillcores and through examination of drillcores and piston cores obtained from a variety of offshore marine geological settings these field and laboratory endeavors have been a major target of the antarctic earth science community for more than thirty years the ross sea sedimentary basins including the byrd basin west antarctica wilkes and pensacola basins east antarctica and the transantarctic mountains provide significant data on the cenozoic glacial record a record that has been traced back to at least 38 ma close to the eocene oligocene boundary this paper reviews the late cenozoic history of the transantarctic mountains and flanking sedimentary basins with emphasis on the debate between the stabilist view of antarctic ice sheet history see clapperton and sugden 1990 and our favored multi glacial dynamic ice sheet model

short term slow slip and correlated tremor episodes in the tokai region central japan 1 we observe the related phenomenon of short term slow slip event sse and low frequency nonvolcanic tremor on the deeper extension of the 1944 tonankai and the anticipated tokai earthquake rupture areas central japan japan nation wide seismometer and tiltmeter array nied hi net has recorded these correlated episodes of sse and tremor known as episodic tremor and slip ets in 2004 and 2005 the events are located on two areas in the tokai region one is near the shima peninsula and the other is around the aichi area both episodes have a typical duration of 2 3 days and released seismic moment corresponding to mw 6 0 moreover these episodes repeatedly occur with a recurrence interval of about six months in both areas this evidence suggests that the coincidence between the sse and the tremor is a characteristic behavior in the whole tremor belt like zone in the nankai trough subduction zone

neogene events in japan and the pacific abstract based on a refined distribution chart of marine molluscan faunas of japan in time and space some key neogene events in japan are discussed with reference to those in the pacific region the mid neogene climatic optimum around 16 ma and a cooling of seawater temperature since 15 ma are considered to be of pan pacific scale the opening of the sea of japan began around 16 ma simultaneously with the climatic optimum two tectonic events the closing of the indonesian seaway and of the central american seaway possibly caused episodes of warm seawater temperatures on the pacific side of japan at 6 ma and 3 ma respectively the izu peninsula on the pacific side of central japan was a volcanic island in the tropical pacific in early miocene time during the northward drift of the island relict species of lepidocyclina manifested an evolutionary change and lasted until 5 ma biotic evolutionary accelerations found in some endemic mollusca of japan since 3 ma are most likely due to phased drops of seawater temperature

paleoceanographic significance of neogene benthic foraminiferal changes in a southwest pacific bathyal depth transect temporal changes in benthic foraminiferal assemblages were quantitatively examined 63 m fraction in four southwest pacific deep sea neogene sequences in a depth transect between approximately 1300 and 3200 m to assist in evaluating paleoceanographic history the most conspicuous changes in benthic foraminiferal assemblages occurred in association with paleoclimatic changes defined at least in part by oxygen isotopic changes the largest centered at 15 ma early middle miocene is represented by an increase in the relative frequencies ofepistominella exigua which underwent a major upward depth migration at that time this was contemporaneous with the well known positive oxygen isotopic shift in the early middle miocene in sites 588 and 590 most of the increase in relative abundances ofe exigua occurred during the middle to later part of the 18o shift following major growth of the east antarctic ice sheet later assemblage changes occurred at 8 5 and 6 5 ma these associations indicate that the benthic foraminiferal assemblages in this depth transect largely adjusted to changes in deep waters related to antarctic cryospheric evolution in general the neogene benthic foraminiferal assemblages in this region underwent little change during the last 23 million years this faunal conservatism suggests that deep sea environments underwent relatively little change in the southwest pacific during much of the neogene although paleoceanographic changes did occur partly in response to high latitude cryospheric evolution these were not of sufficient magnitude to create major deep sea faunal changes in this part of the ocean the benthic foraminiferal assemblages are dominated by individuals smaller than 150 m most taxonomic turnover occurred in the larger 150 m size fractions

the middle miocene climatic transition east antarctic ice sheet development deep ocean circulation and global carbon cycling abstract the middle miocene represents a major change in state in cenozoic climatic evolution following the climax of neogene warmth in the late early miocene at 16 ma the early stage of this climatic transition from 16 to 14 8 ma was marked by major short term variations in global climates east antarctic ice sheet eais volume sea level and deep ocean circulation in the later stage from 14 8 to 12 9 ma climatic developments included major growth of the eais and associated antarctic cooling a distinct increase in the meridional temperature gradient large fluctuations in sea level followed by a global sea level fall and important changes in deep water circulation including increased production of southern component water east antarctic ice sheet growth and polar cooling also had large effects on global carbon cycling and on the terrestrial biosphere including aridification of mid latitude continental regions increased stability of the eais after 14 8 ma represents a crucial step in the establishment of late neogene global climate systems what controlled these changes in polar climates and the east antarctic ice sheet deep ocean circulation changes probably played a major role in the evolution and variation in polar climates as they have throughout the cenozoic oxygen and carbon isotopic evidence for warm saline deep water production in the eastern tethyan northern indian ocean indicates that meridional heat transport to the antarctic inhibited cenozoic polar cooling and eais growth during the early middle miocene from 16 to 14 8 ma inferred competition between warm low latitude sources derived from the eastern tethyan northern indian ocean and a cold high latitude source southern component water from 16 to 14 8 ma may have been associated with instability in the antarctic climate and cryosphere reduction of warm saline deep water flow to the southern ocean at 14 8 ma may have decreased meridional heat transport to the antarctic cooling the region and leading to increased production of southern component water these middle miocene climatic and cryospheric changes in the antarctic had profound effects on marine and terrestrial climates as the meridional surface temperature gradient increased boundaries between climatic zones strengthened leading to increased aridification of mid latitude continental regions in australia africa and north and south america enhancing the development of grasslands and stimulating the evolution of grazing mammals

the evolution of miocene climates in north china preliminary results of quantitative reconstructions from plant fossil records the miocene climate evolution in north china is preliminarily discussed by means of comparisons in seven climate parameters quantitatively reconstructed by the coexistence approach on 34 selected macro and microfloras over north china the miocene temperatures show no great difference in the western and eastern part of north china temperature fluctuations particularly in mean annual temperature are found within floras from several sites the fluctuation pattern from a climate optimum in the mid miocene to cooling decline in the late miocene is generally consistent with the global trend of miocene temperature change the reconstructed precipitation from all the sites studied shows much wetter conditions in north china during the miocene than at present which corroborates the results from paleoprecipitation proxy of fossil mammals like the situation in paleo temperature the miocene precipitation from north china shows no distinct difference between the western and eastern regions it is suggested that north china particularly in the western part was by no means under an arid or semi arid environment during the miocene north china is an ideal region for study of the impact of the east asian monsoon system however the pattern of precipitation change derived from the monsoon index msh and mean annual precipitation map shows contradictory results therefore there appears no definite conclusion on when the east asian summer monsoon intensified possible reasons for inconsistency in temperature and precipitation changes are discussed directions of future work to improve the resolution of climate evolution are also pointed out c 2010 elsevier b v all rights reserved

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

sedimentological evidence for the formation of an east antarctic ice sheet in eocene oligocene time middle eocene to late oligocene sediments recovered at ocean drilling program sites 689 and 690 on maud rise in the southernmost atlantic ocean and at sites 738 and 744 on kerguellen plateau in the southernmost indian ocean were analysed in order to study the depositional environment and the palaeoclimate special emphasis was placed on the reconstruction of the formation of a cryosphere on the antarctic continent the investigations include quantifications of carbonate and opal contents grain size analyses and studies of clay mineral assemblages the sedimentary sequence at all sites under investigation is highly pelagic with nannofossil oozes and chalks dominant the first indication of probable glacierization at sea level is in the form of isolated gravel and terrigenous sand grains which indicate ice rafting from middle eocene time at c 45 5 ma this is supported by enhanced concentrations of detrital chlorite and reworked kaolinite probably some glaciers reached the sea while most of the continent remained under the influence of a humid and warm to temperate climate the growth of the inland ice resulted in enhanced physical weathering and in increased contents of detrital chlorite and kaolinite from about 40 ma a strengthening of the glacial conditions and the onset of continental east antarctic glaciation is recorded in early oligocene sediments with an age of 36 ma all major sediment parameters document this event the clay mineralogy changed between c 36 3 ma and c 35 5 ma from smectite dominated assemblages to illite and chlorite dominated assemblages the latter being indicative of physical weathering under cooler climates large quantities of ice rafted gravel and sand accumulated on the kerguelen plateau between 36 0 ma and 35 8 ma at the same time an increase in opal content occurred as well as a decrease in carbonate the sediment parameters imply that the east antarctic continent was more or less totally buried beneath the ice during oligocene time the ice sheet however probably did not have a polar but a temperate character as indicated by the occurrence of nothofagus and relatively warm surface water temperatures prohibiting the long distance transport of debris by icebergs

paleo eolian dynamics in the andean plateau inferences from sedimentology of fossil and modern dunes fil lopez steinmetz romina lucrecia universidad nacional de jujuy instituto de ecorregiones andinas consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet salta instituto de ecorregiones andinas argentina universidad nacional de jujuy argentina consejo nacional de investigaciones cientificas y tecnicas argentina

first record of middle miocene marine diatoms from the colombian pacific nw south america and their paleoceanographic significance abstract middle miocene marine diatoms have been reported in the eastern equatorial pacific by the deep sea drilling project dsdp the ocean drilling program odp and the integrated ocean drilling program iodp few studies however have been completed on onshore sections from south america vallejo et al 2006 published the biostratigraphy of the ladrilleros juanchaco section on the northwest pacific colombian coast utilizing calcareous nannofossils planktonic foraminifera and diatoms in this work we present in detail the study of marine diatoms of that section in order to understand their implications with the age model proposed and provide a paleoceanographic interpretation the diatom recovery is restricted to two intervals at the top of the miocene sequence two biozones from the low latitude zonation can be recognized from base to top they are 1 the coscinodiscus lewisianus zone which contains the same species assemblage reported in antofagasta coastal sediments chile and 2 the craspedodiscus coscinodiscus zone we found that the diatoms represent older ages than proposed by calcareous nannofossils these different ages suggest diachronism between the events of microfossil groups nevertheless in a new interpretation of the distribution patterns of calcareous nannofossils in the upper part of the section the diatom age model could be synchronous the high abundance of thalassionema nitzschioides and thalassiothrix longissima reveal cool upwelling rich oceanic waters at the top of the sequence as well as an increase in paleoproductivity suggested by an increase of rhizosolenia spp and t longissima mats cool water trends support a strengthening of the peru chile current actinoptychus sp leptocylindrus danicus and paralia sulcata point to a nearshore environment the common occurrence of fresh water continental diatoms and palm silicophytoliths indicate an increased input of continental material since ichnofossils and benthic foraminifera reveal ocean depths below 1000 m this change may have related to hyperpycnal flows

chemical and physical erosion rhythms of the west african cenozoic morphogenesis the 39 ar 40 ar dating of supergene k mn oxides chemical weathering and mechanical erosion are first order processes of long term tropical morphogenesis which is still poorly deciphered for lack of time constraints we address this issue by laser probe 39ar 40ar dating of generations of cryptomelane k1 2mn8o16 nh2o from the manganese ore deposit of tambao in northern burkina faso this mn deposit results from the supergene weathering of carbonate and silicate mn protores underneath lateritic palaeolandsurfaces it consists of an upper cryptomelane rich domain and a lower domain where pyrolusite b mno2 is the dominant mn oxide the oldest 39ar 40ar ages 59 45 ma are obtained on surface outcrops while the youngest ones characterize deep oxidation fronts 3 4 2 9 ma apparent correlations of 39ar 40ar age groups with d18o and eustatic curves allow definition of the different stages of morphogenesis paleocene eocene ages 59 45 ma bracket a greenhouse period propitious to bauxitic weathering the lack of significant ages between 45 and 29 ma characterizes a period dominated by mechanical erosion during which detrital sediments including lateritic materials were accumulated in intracratonic basins allowing the exhumation of a new lateritic landsurface two major weathering periods separated by a second erosion episode 24 18 ma are also depicted at the end of oligocene 29 24 ma and lower to mid miocene 18 11 5 ma in the upper domain during which newly shaped land surfaces conspicuously weathered the shorter weathering and erosion episodes recorded in the lower domain from 18 to 2 9 ma led to the final geomorphic changes that were conducive to the formation of glacis the preservation of old cryptomelane 59 45 ma in the upper part of the ore deposit indicates a cenozoic denudation limited to the erosion of previous bauxites and partly of ferricretes

phytoliths at dsdp site 591 in the southwest pacific and the aridification of australia phytoliths found in deep sea sediments at dsdp site 591 in the southwest pacific reflect the onset and progress of aridification on the australian continent from the middle miocene to early pleistocene 14 4 1 0 ma bp including a maximum of aridity in the late pliocene the process can be attributed to the northward drift of the australian plate the growth of southern and northern hemisphere ice sheets and related developments in the global wind system

early and middle miocene stable isotopes implications for deepwater circulation and climate the middle miocene 18o increase represents a fundamental change in the ocean atmosphere system which like late pleistocene climates may be related to deepwater circulation patterns there has been some debate concerning the early to early middle miocene deepwater circulation patterns specifically recent discussions have focused on the relative roles of northern component water ncw production and warm saline deep water originating in the eastern tethys our time series and time slice reconstructions indicate that ncw and tethyan outflow water two relatively warm deepwater masses were produced from 20 to 16 ma ncw was produced again from 12 5 to 10 5 ma another feature of the early and middle miocene oceans was the presence of a high 13c intermediate water mass in the southern hemisphere which apparently originated in the southern ocean miocene climates appear to be related directly to deepwater circulation changes deep waters warmed in the early miocene by 3 c 20 to 16 ma and cooled by a similar amount during the middle miocene 18o increase 14 8 to 12 6 ma corresponding to the increase 20 ma and subsequent decrease 16 ma in the production of ncw and tethyan outflow water large 0 6 relatively rapid 0 5 m y 18o increases in both benthic and planktonic foraminifera i e the mi zones of miller et al 1991a and wright and miller 1992a were superimposed in the long term deepwater temperature changes they are interpreted as reflecting continental ice growth events seven of these m y glacial interglacial cycles have been recognized in the early to middle miocene two of these glacial interglacial cycles mi3 and mi4 combined with a 2 to 3 c decrease in deepwater temperatures to produce the middle miocene 18o shift

mid miocene isotope stratigraphy in the deep sea high resolution correlations paleoclimatic cycles and sediment preservation mid miocene pelagic sedimentary sections can be correlated using intermediate and high resolution oxygen and carbon isotopic records of benthic foraminifera precision of a few tens of thousands of years is readily achievable at sites with high sedimentation rates for example deep sea drilling project sites 289 and 574 the mid miocene carbon isotope records are characterized by an interval of high 13c values between 17 and 13 5 ma the monterey excursion of vincent and berger 1985 upon which are superimposed a series of periodic or quasi periodic fluctuations in 13c values these fluctuations have a period of approximately 440 kyr suggestive of the 413 kyr cycle predicted by milankovitch theory vincent and berger proposed that the monterey excursion was the result of increased organic carbon burial in continental margins sediments the increased 13c values called 13c maxima superimposed on the generally high mid miocene signal coincide with increases in 18o values suggesting that periods of cooling and or ice buildup were associated with exceptionally rapid burial of organic carbon and lowered atmospheric co2 levels it is likely that during the monterey excursion the ocean atmosphere system became progressively more sensitive to small changes in insolation ultimately leading to major cooling of deep water and expansion of continental ice we have assigned an absolute chronology based on biostratigraphic and magneto biostratigraphic datum levels to the isotope stratigraphy and have used that chronology to correlate unconformities seismic reflectors carbonate minima and dissolution intervals intervals of sediment containing 13c maxima are usually better preserved than the overlying and underlying sediments indicating that the 13c values of tco2 in deep water and the corrosiveness of seawater are inversely correlated this again suggests that the 13c maxima were associated with rapid burial of organic carbon and reduced levels of atmospheric co2 the absolute chronology we have assigned to the isotopic record indicates that the major mid miocene deepwater cooling ice volume expansion took 2 m y and was not abrupt as had been reported previously the cooling appears abrupt at many sites because the interval is characterized by a number of dissolution intervals the cooling was not monotonic and the 2 m y interval included an episode of especially rapid cooling as well as a brief return to warmer conditions before the final phase of the cooling period the increase in 18o values of benthic foraminifera between 14 9 and 12 9 ma was greatest at deeper water sites and at sites closest to antarctica the data suggest that the 18o value of seawater increased by no more than about 1 1 per mil during this interval and that the remainder of the change in benthic 18o values resulted from cooling in antarctic regions of deepwater formation equatorial planktonic foraminifera from sites 237 and 289 exhibit a series of 0 4 per mil steplike increases in 13c values only one of these increases in planktonic 13c is correlated with any of the features in the mid miocene benthic carbon isotope record

relations between monterey formation deposition and middle miocene global cooling naples beach section california an oxygen and carbon isotopic stratigraphy has been established for the miocene monterey formation 18 to 8 ma at naples beach santa barbara county california correlation to the deep sea climatic record provides a test of the monterey hypothesis which suggests that organic carbon rich deposition in the monterey formation fostered middle miocene global cooling through drawdown of atmospheric partial co 2 oxygen isotopic correlation of the naples beach section to the deep sea record suggests that increased organic carbon rich deposition coincided closely with deep water cooling and major east antarctic ice sheet growth from 14 5 to 14 1 ma and with a 13 c maximum in deep sea records these results support a corollary of the monterey hypothesis that episodic organic carbon rich deposition within the monterey formation contributed to deep sea 13 c maxima and to synchronous global cooling

a revised and improved age model for the middle miocene part of iodp site u1318 porcupine basin offshore southwestern ireland integrated ocean drilling program leg 307 site u1318 is one of the few relatively complete middle miocene drillcores from the north atlantic porcupine basin offshore southwestern ireland using benthic foraminiferal stable carbon and oxygen isotopes the existing age model for site u1318 was improved the stable isotope record displays globally recognized isotope events used to revise the existing magnetostratigraphy based age model two intervals contained misidentified magnetochrons which were corrected the sampled interval now has a refined age of 12 75 16 60 ma with a temporal resolution of c 29 ka

distribution and genesis of bauxite on the mambilla plateau se nigeria abstract only small low grade occurrences of bauxite are known in nigeria associated with ferricretes on the jos plateau widespread bauxite has been discovered on the mambilla plateau laterite is developed on gneisses and basalt while on trachytic parent rocks low silica bauxite occurs with a thickness of more than 5 m and covering an area of at least 1 km2 this bauxite consists of gibbsite and goethite in contrast to the ferricretes of the jos plateau weathering on the mambilla plateau led to the formation of stone line profiles ferricretes were developed on the upper jurassic gondwana surface under contrasting climate and are preserved as relicts in the southern part of the mambilla plateau where weathered precambrian basement occurs in a highly uplifted position dismantling of these ferricretes is attributed to a gradual change of paleoclimate towards more humid conditions after the extrusion of volcanic rocks in the northern part of the plateau presumably during lower to mid miocene these volcanics underwent intense chemical weathering bauxite and laterite formed depending on the type of parent rock weathering profiles are mostly truncated and overlain by reworked material allochthonous components occur both within and also below the stone line this is shown by mineralogical indicators such as ilmenite or quartz and by a shift in the zr ti ratio similar profiles are missing further north on the jos plateau where ferricretes formed instead this is attributed to regional differences in paleoclimatic conditions which were more humid at mambilla while jos was under the influence of dryer conditions the widespread formation of laterite on different parent rocks on the mambilla plateau could be related to a global mid miocene climatic optimum which led to a general intensification of chemical weathering processes

tertiary ice sheet dynamics the snow gun hypothesis we observe strong negative correlation between tertiary low to mid latitude planktonic foraminiferal 18o and the difference between these data and coeval benthic foraminiferal 18o late quaternary data do not show this correlation coupling statistical model 18o comparisons and evidence for antarctic ice and ocean temperature variation we infer that tertiary ice volume recorded by tropical planktonic 18o increased as the deep ocean warmed because the isotopic signatures of deepwater temperature variation and ice volume change were of opposite sign the sum of these signals in tertiary benthic 18o became lost in the noise this renders low correlation between tertiary planktonic and benthic 18o time series compared to late quaternary data we contend that tertiary ice sheet growth was commonly driven by warming of deep water from low to mid latitude marginal seas snow gun hypothesis in contrast late quaternary ice sheets grew as deep water formed at high latitude cooled because tectonic forcing and orbital forcing at low latitude primarily controlled production and temperature variations of this warm saline deep water these influences largely dictated tertiary ice volume fluctuations through the tertiary we infer ice volume fluctuations to be an important component of sea level history on timescales between 103 and 107 years

the cenozoic record of continental mineral deposition on broken and ninetyeast ridges indian ocean southern african aridity and sediment delivery from the himalayas the mineral component of pelagic sediments recovered from the indian ocean provides both a history of eolian deposition related to climatic changes in southern africa and a record of terrigenous input related to sediment delivery from the himalayas a composite cenozoic dust flux record from four sites in the central indian ocean is used to define the evolution of the kalahari and namib desert source regions the overall record of dust input is one of very low flux for much of the cenozoic indicating a long history of climate stability and regional hyperaridity the most significant reduction in dust flux occurred near the paleocene eocene boundary and is interpreted as a shift from semiarid climates during the paleocene to more arid conditions in the early eocene further aridification is recorded as stepwise reductions in the input of dust material which occur from about 35 to 40 ma 27 to 32 ma and 13 to 15 ma and correlate to significant enrichments in benthic foraminifer 18o values the mineral flux in sediments from the northern indian ocean site 758 records changes in the terrigenous input apparently related to the erosion of the himalayas and indicates a rapid late cenozoic uplift history three major pulses of increased terrigeneous sediment flux are inferred from the depositional record the initial increase began at about 9 5 ma and continued for roughly 1 0 million years a second pulse with approximately the same magnitude occurred from about 7 0 to 5 6 ma the largest pulse of enhanced terrigenous influx occurred during the pliocene from about 3 9 to 2 0 ma when average flux values were severalfold greater than at any other time in the cenozoic

miocene stable isotope record a detailed deep pacific ocean study and its paleoclimatic implications deep sea drilling project site 289 in the western equatorial pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the miocene deep ocean the isotopic record reflects major changes in paleoclimate and paleoceanography probably dominated by a major phase of antarctic ice cap growth the transition from a relatively unglaciated world to one similar to today occurred between 16 5 x 10 6 and 13 x 10 6 years before the present with the greatest change occurring between approximately 14 8 x 10 6 and 14 0 x 10 6 years before the present

paleoseawater density reconstruction and its implication for cold water coral carbonate mounds in the northeast atlantic through time carbonate buildups and mounds are impressive biogenic structures throughout earth history in the recent ne atlantic cold water coral cwc reefs form giant carbonate mounds of up to 300 m of elevation the expansion of these coral carbonate mounds is paced by climatic changes during the past 2 7 myr environmental control on their development is directly linked to controls on its main constructors the reef building cwcs seawater density has been identified as one of the main controlling parameter of cwc growth in the ne atlantic one possibility is the formation of a pycnocline above the carbonate mounds which is increasing the hydrodynamic regime supporting elevated food supply and possibly facilitating the distribution of coral larvae the potential to reconstruct past seawater densities from stable oxygen isotopes of benthic foraminifera has been further developed a regional equation gives reliable results for three different settings peak interglacials e g holocene peak glacials e g last glacial maximum and intermediate setting between the two extremes seawater densities are reconstructed for two different ne atlantic cwc carbonate mounds in the porcupine seabight indicating that the development of carbonate mounds is predominantly found at a seawater density range between 27 3 and 27 7 kg m 3 notation comparable to recent conditions we interpret the reconstructed density range as a pycnocline serving as boundary layer on which currents develop carrying nutrition and possibly coral larvae the close correlation of cwc reef growth with reconstructed seawater densities through the pleistocene highlights the importance of pycnoclines and intermediate water mass dynamics

internal structure of mount merapi indonesia derived from long offset transient electromagnetic data 1 a long offset transient electromagnetic lotem survey was carried out on merapi volcano indonesia in 1998 lotem data have been recorded at 41 receiver locations which cover a 10 km w e and a 15 km s n profile the signals were transmitted at four locations on the south west and north sides of merapi the data were interpreted with one dimensional 1 d inversions in addition two particular features were investigated with 3 d modeling on the south flank the magnetic field data show strong 3 d distortions consistently over the profile which can only be explained by a conductive near surface structure like a fracture filled with conductive fluids the simulation of topographic effects shows that the interpretation is not significantly affected on both profiles the most striking feature is a conductive layer of 20 m at depths of 500 1000 m below the surface and a thickness of 1 2 km the cause of the increased conductivity may be different for the summit area the intermediate zone and at the flanks below the summit in vicinity of the conduit the decrease in resistivity is produced either by hydrothermal fluids by partial melts or rocks altered by the hydrothermal system or by a combination in the intermediate zone between the conduit and the flanks either alteration or hydrothermal fluids may be the source of the conductivity increase fluids seem to be the most likely cause for the conductive layer at the flanks and the west east striking anomaly from the resistivity of the conductive layer and the typical porosity of volcanic rock we estimate fluid resistivities of 0 2 1 m

pliocene paleoclimate and east antarctic ice sheet history from surficial ash deposits the preservation age and stratigraphic relation of an in situ ashfall layer with an underlying desert pavement in arena valley southern victoria land indicate that a cold desert climate has persisted in arena valley during the past 4 3 million years these data indicate that the present east antarctic ice sheet has endured for this time and that average temperatures during the pliocene in arena valley were no greater than 3 c above present values one implication is that the collapse of the east antarctic ice sheet due to greenhouse warming is unlikely even if global atmospheric temperatures rise to levels last experienced during mid pliocene times

miocene deepwater oceanography a global synthesis of miocene benthic foraminiferal carbon and oxygen isotopic and faunal abundance data indicates that miocene thermohaline circulation evolved through three regimes corresponding approximately to early middle and late miocene times there is evidence for major qualitative differences between the circulation of the modern ocean and the miocene ocean prior to 11 ma the 13c 12c ratios of the benthic foraminifera cibicidoides are interpreted in terms of water mass aging i e the progressive depletion of dissolved o2 and lowering of 13c values as the result of oxidation of organic matter as water flows further from its sources at the surface of the oceans both isotopic and faunal data indicate that the early miocene regime from 22 to 15 ma was the most different from today s during that interval intermediate and deep waters of both the atlantic and the pacific oceans aged in a northward direction and the intermediate waters of the indian the south atlantic and the south pacific oceans were consistently the youngest in the global ocean we speculate that early miocene global thermohaline circulation may have been strongly influenced by the influx of warm saline water tethyan indian saline water from the tethys into the northern indian ocean the isotopic and faunal data suggest that flow from the tethyan region into the indian ocean diminished or terminated at about 14 ma isotopic and faunal data give no evidence for north atlantic deep water nadw formation prior to about 14 5 ma with the exception of a brief episode in the early miocene from 14 5 to 11 ma nadw formation was weak and circumpolar and antarctic water flooded the deep south atlantic and south pacific as the antarctic ice cap grew from about 10 ma to the end of the miocene thermohaline circulation resembled the modern circulation in many ways in latest miocene time 6 to 5 ma circulation patterns were very similar to today s except that nadw formation was greatly diminished the distribution pattern of siliceous oozes in miocene sediments is consistent with our proposed reconstruction of thermohaline circulation major changes which occurred in circulation during the middle miocene were probably related to the closing of the tethys and may have contributed to rapid middle miocene growth of the antarctic ice cap appendices 1 4 6 and 7 are available withentire article on microfiche order fromamerican geophysical union 2000 floridaavenue n w washington dc 20009 document 88p 002 5 00 payment mustaccompany order

paleoceanographic implications of miocene deep sea hiatuses miocene paleoceanographic evolution exhibits major changes resulting from the opening and closing of passages the subsequent changes in oceanic circulation and development of major antarctic glaciation the consequences and timing of these events can be observed in variations in the distribution of deep sea hiatuses sedimentation patterns and biogeographic distribution of planktic organisms the opening of the drake passage in the latest oligocene to early miocene 25 20 ma resulted in the establishment of the deep circumpolar current which led to thermal isolation of antarctica and increased global cooling this development was associated with a major turnover in planktic organisms resulting in the evolution of neogene assemblages and the eventual extinction of paleogene assemblages the erosive patterns of two widespread hiatuses ph 23 0 22 5 ma and nh 1 20 18 ma indicate that a deep circumequatorial circulation existed at this time characterized by a broad band of carbonate ooze deposition siliceous sedimentation was restricted to the north atlantic and a narrow band around antarctica a major reorganization in deep sea sedimentation and hiatus distribution patterns occurred near the early middle miocene boundary apparently resulting from changes in oceanic circulation beginning at this time deep sea erosion occurred throughout the caribbean hiatus nh 2 16 15 ma suggesting disruption of the deep circumequatorial circulation and northward deflection of deep currents and or intensification of the gulf stream sediment distribution patterns changed dramatically with the sudden appearance of siliceous ooze deposition in the marginal and east equatorial north pacific by 16 0 to 15 5 ma coincident with the decline of siliceous sedimentation in the north atlantic this silica switch may have been caused by the introduction of norwegian overflow water into the north atlantic acting as a barrier to outcropping of silica rich antarctic bottom water the main aspects of the present oceanic circulation system and sediment distribution pattern were established by 13 5 to 12 5 ma hiatus nh 3 coincident with the establishment of a major east antarctic ice cap antarctic glaciation resulted in a broadening belt of siliceous ooze deposition around antarctica increased siliceous sedimentation in the marginal and east equatorial north pacific and indian oceans and further northward restriction of siliceous sediments in the north atlantic periodic cool climatic events were accompanied by lower eustatic sea levels and widespread deep sea erosion at 12 to 11 ma nh 4 10 to 9 ma nh 5 7 5 to 6 2 ma nh 6 and 5 2 to 4 7 ma nh 7

early oligocene ice sheet expansion on antarctica stable isotope and sedimentological evidence from kerguelen plateau southern indian ocean sedimentological and stable isotope data from a pelagic sequence recovered from the southern indian ocean provide the most convincing evidence to date for short term expansion of a large ice sheet on antarctica during the earliest oligocene 36 ma terrigenous debris identified as ice rafted in origin on the basis of textural compositional and size criteria is present at the same stratigraphic level as the ubiquitous early oligocene oxygen isotope shift the highest benthic foraminiferal 18o values 3 0 of the paleogene occur in samples from within the ice rafted debris interval these values are similar to those recorded by holocene benthic foraminifera implying that the ice sheet may have attained a volume similar to that of the present day ice sheet on antarctica the stratigraphic distribution of ice rafted debris and high oxygen isotope values indicate that these conditions persisted for roughly 100 ka

sr isotopic paleomagnetic and biostratigraphic calibration of horse evolution evidence from the miocene of florida during the middle miocene an explosive adaptive radiation resulted in the advent of grazing horses with high crowned teeth in north america new sr isotopic paleomagnetic and biostratigrahic evidence from the miocene marine and nonmarine sequence of the florida panhandle calibrates the base of this adaptive radiation the transition from the primitive outgroup species parahippus leonensis to the most primitive high crowned horse merychippus gunteri occured after about 17 7 ma after this event the lowest known stratigraphic level at which diversification i e presence of two or more sympatric species of grazing merychippine horses occurs is about 16 2 ma or within the early part of chron c5br although this currently is the only sequence where the parahippine merychippine transition is directly calibrated biochronologic evidence from other important contemporaneous localities in texas nebraska and california indicate that diversification occured rapidly throughout north america between 15 and 16 ma

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

origin and age of phosphorite from the south central florida platform relation of phosphogenesis to sea level fluctuations and δ13c excursions abstract francolite carbonate fluorapatite from predominantly peloidal phosphorite grains in the miocene hawthorn group from the babcock deep core southwestern florida is highly substituted with an average composition of ca4 61na0 22mg0 14k0 05sr0 02 po4 2 23 co3 0 62 so4 0 12 f 1 04 13c values of 1 0 7 8 pdb of the francolite co3 indicate a substantial contribution of c from an organic source the sulfur isotopic composition of francolite so4 is depleted to slightly enriched relative to miocene seawater and suggests that phosphogenesis occurred during early burial diagenesis in organicrich sediments above or in the zone of sulfate reduction the uniformly high sr na mg so4 and co3 contents of the francolite the 18o values of the francolite co3 0 2 4 2 pdb and the inclusion of pyrite and organic matter in phosphorite grains suggest that the francolite has had minimal chemical alteration since its formation phosphorite from the babcock deep core has sr 87 86 ratios that range from 0 708148 0 708880 and sr derived ages that range from late oligocene 25 6 0 7 ma to early late miocene 9 2 1 4 ma the sr derived ages of relatively fragile calcareous benthic foraminifers are consistently younger than associated hard tightly cemented phosphorite and support textural evidence of extensive reworking the age of the host sediment ranges from early miocene to pliocene and its depositional history is related to sea level fluctuations approximately three quarters of the total phosphorite in the babcock deep core formed during or within 2 my before the major early to mid miocene positive 13cshift as recorded at dsdp site 588 southwest pacific one third of the total phosphorite formed just prior to the carbon shift in the short interval between 21 9 and 20 4 ma these results indicate that reworked phosphorite deposits may provide a proxy of organic carbon cycling on continental shelves that correspond to sealevel fluctuations and to variations in the 13crecord

global warming and rainfall lessons from an analysis of mid miocene climate data abstract the mid miocene climatic optimum mmco has been regarded as an analog for future global warming due to its scale of warming being equivalent to the warming predicted for the next century by the international panel on climate change ipcc s fourth report however little is known about how the mmco influenced paleoprecipitation in central china in this study two pollen floras from the eastern longzhong basin northern central china were quantitatively analyzed to reconstruct the climatic conditions likely during the mmco the paleoclimatic parameters obtained by applying the coexistence approach coa to these two palynological assemblages showed that the mean annual temperature mat 16 6 c for the mmco was 5 7 c higher than the present day mat 10 9 c and that mean annual precipitation map 955 4 mm was 413 5 mm higher than at present 541 9 mm indicating a much warmer and wetter climate the higher mean temperature for the coldest month cmt and the minimum monthly precipitation mimp values also indicate a warmer and wetter coldest and driest month respectively and thus suggest the prevalence of a more balanced seasonal paleoclimate in northern central china these climatic conditions are equivalent to higher global temperatures of 5 6 c during the mmco this finding would imply that precipitation in northern central china will increase in the context of ongoing global warming