synchronizing terrestrial and marine records of environmental change across the eocene oligocene transition records of terrestrial environmental change indicate that continental cooling and or aridification may have predated the greenhouse icehouse climate shift at the eocene oligocene transition eot by ca 600 kyr in north america marine terrestrial environmental change asynchronicity is inferred from a direct comparison between the astronomically tuned marine eot record and published 40ar 39ar geochronology of volcanic tuffs from the white river group wrg sampled at flagstaff rim wyoming and toadstool geologic park nebraska which are type sections for the chadronian and orellan north american land mammal ages we present a new age model for the wrg underpinned by high precision 206pb 238u zircon dates from 15 volcanic tuffs including six tuffs previously dated using the 40ar 39ar technique weighted mean zircon 206pb 238u dates from this study are up to 1 0 myr younger than published anorthoclase and biotite 40ar 39ar data calibrated relative to fish canyon sanidine at 28 201 ma giving consideration to the complexities strengths and limitations associated with both the 40ar 39ar and 206pb 238u datasets our interpretation is that the recalculated 40ar 39ar dates are anomalously old and the 206pb 238u zircon dates more accurately constrain deposition 206pb 238u calibrated age depth models were developed in order to facilitate a robust intercomparison between marine and terrestrial archives of environmental change and indicate that i early orellan terrestrial cooling recorded at toadstool geologic park was synchronous with the onset of early oligocene antarctic glaciation and ii the last appearance datums of key chadronian mammal taxa are diachronous by ca 0 7 myr between central wyoming and nw nebraska

pedogenic carbonate carbon isotopic constraints on paleoprecipitation evolution of desert in the pacific northwest usa in response to topographic development of the cascade range abstract the cascade range in the northwestern u s acts as an orographic barrier to the easterly movement of humid air masses from the pacific ocean producing a massive rain shadow with arid to semi arid climate conditions on the leeward side of the range pedogenic carbonates formed in the c3 dominated landscapes east of the range have 13ccarbonate that is enriched by approximately 4 relative to carbonates formed in sub tropical c3 dominated ecosystems we measured stable isotopic compositions of pedogenic carbonates preserved in the quaternary and neogene sedimentary rock units in the inland pacific northwest and examined the impact of long term aridification and paleohydrology on their isotopic compositions the determined 13ccarbonate record shows a gradual increase of 5 from approximately 10 in older pedogenic carbonates to 5 in younger ones whereas 18ocarbonate record indicates a decrease of approximately 4 in the late neogene in addition the quaternary 13ccarbonate and 18ocarbonate records indicate the highest 13c and 18o among the samples during the pleistocene and significant fluctuation over the time period the gradual increase in the 13ccarbonate and the decrease in the 18ocarbonate in the late neogene are interpreted by the development of the rain shadow as a result of topographic development of the cascade range changes in the quaternary isotope records suggest a decrease in regional precipitation and isotopically depleted winter precipitation resulting from changes in large scale atmospheric circulation patterns due to advance and retreat of northern hemisphere continental ice sheet the isotope record from pedogenic carbonates provides a direct record of climatic change suggesting that long term carbon isotope data can provide useful constraints on timing and intensity of regional desertification and its associated climate and topographic interaction

origin and development of artemisia asteraceae in asia and its implications for the uplift history of the tibetan plateau a review abstract the spatial and temporal evolution of artemisia and its relationship with the tibetan plateau tp uplift are examined by summarizing pollen data from 122 sites across china the pollen morphological data reveal that artemisia may have originated from the arid semiarid middle latitudes of asia in the late eocene and spread west and east in the oligocene as the result of early uplift of the tibetan plateau and the global cooling during the miocene artemisia reached the southeastern part of the tp and became common in the western tp due to the high elevation in these regions at the same time the asian monsoon prevented the spread of artemisia to the southern part of the tp since the pliocene especially in the pleistocene artemisia distribution was very similar to its current distribution which indicates that the topography of the tp and the paleoenvironmental conditions in the east asia became more like today thus the cenozoic origin and evolution of artemisia in the asia was strongly influenced by the uplift of the tp global cooling as well as monsoon development

tectonic significance of paleobotanically estimated climate and altitude of the late eocene erosion surface colorado erosion beveled the laramide front range uplift in colorado to a surface of low relief by the end of the eocene this study uses j a wolfe s new multivariate climate analysis techniques to determine the paleoelevation of this regional surface by examining the overlying 35 ma florissant flora a multiple regression model explaining 93 3 of the variance in mean annual temperature was developed using wolfe s dataset of 31 leaf physiognomic character states for 86 modern vegetation sites these character states were scored on 29 species collected from one facies of the florissant lake beds the paleotemperature estimate of mean annual temperature 10 7 plus minus 1 5c derived from these data when combined with sea level temperature and terrestrial lapse rate implies a late eocene paleoelevation of 2 4 2 7 km pliocene uplift is thus not required to explain the present elevation of 2 5 km it is unclear when and why the southern rocky mountains achieved this elevation magmatic crustal thickening can explain the late eocene high elevation of the southern rockies but neither this mechanism nor compressive thickening explains why the great plains which are tied to the florissant elevation by the wall mountain tuff were also high this paleoelevation estimate indicates that regional surfacesmore of planation could be formed at high elevation in the eocene probably because of peculiarities of the eocene climate less

stable isotope compositions of herbivore teeth indicate climatic stability leading into the mid miocene climatic optimum in idaho u s a abstract the effects of global climate change are manifested at the regional level consequently evaluation of links between palaeoenvironmental change and turnover of past biotas must use regional scale climate data here we test whether climate change influenced faunal and floral patterns leading up to and during the mid miocene climatic optimum mmco based on datasets collected in the railroad canyon section rcs central eastern idaho u s a specifically we use isotope compositions of herbivore tooth enamel to investigate how mean annual precipitation map mean annual temperature mat cold month mean temperature cmmt and temperature seasonality varied through the rcs and how this local record compares to global climate reconstructions isotope compositions of teeth from the fossil equid merychippus and rhinocerotid diceratherium were compared across five time bins from c 23 to c 15 ma bulk 18o values of both taxa indicate that meteoric water compositions were unchanged through the study interval consistently c 15 6 but were c 1 9 higher than current regional meteoric water this difference points to warmer climates in central eastern idaho during the miocene post middle miocene topographic uplift in western north america and or shifts to air mass trajectories serial sampling of enamel shows seasonal fluctuations in water compositions and temperature bulk 13c values indicate an average map of 190 range 10 510 mm yr 1 with no significant change through the study interval comparable to today s map 236 mm yr 1 the reconstructed semi arid seasonal warm climate for the rcs agrees with phytolith assemblage data from the same strata indicating dominantly open grassy habitats however it is inconsistent with previously held ideas of warm wet mid miocene climates in the northern rocky mountains nrm based on paleosol analyses our inferred stable climate conditions for the mmco of the nrm contrast with coeval records from europe and asia indicating sustained or enhanced warm and wet climates these differences point to a decoupling of regional climate from global trends and highlight the necessity of studying regional variation to understand the biotic impacts of global climate change

global vegetation dynamics and latitudinal temperature gradients during the mid to late miocene 15 97 5 33 ma a 617 site palaeobotanical dataset for the mid to late miocene is presented this dataset is internally consistent and provides a comprehensive overview of vegetational change from 15 97 to 5 33 ma the palaeobotanical dataset has been translated into the biome4 classification scheme to enable direct comparison with climate model outputs the vegetation change throughout the langhian seravallian tortonian and messinian is discussed the data shows that the langhian which includes the end of the mid miocene climatic optimum represents a world significantly warmer than today the high northern latitudes were characterised by cool temperate forests the mid latitudes by warm temperate mixed forests the tropics by tropical evergreen broadleaf forests and antarctica by tundra shrub vegetation cool temperate mixed forest existed during the seravallian in the high northern latitudes a reduction in warm temperate mixed forests in the mid latitudes and a loss of tundra on antarctica was noted tortonian vegetation distribution indicates that further cooling had occurred since the seravallian the major changes in vegetation include the first evidence for cold taiga forest in the high northern latitudes and a further reduction of warm temperate mixed forests by the messinian this cooling trend had eliminated warm temperate mixed forests from the western usa and australia and had formed mid latitude deserts despite the cooling trend throughout the mid to late miocene the vegetation distribution of all four reconstructed stages reflect the vegetation of a world warmer than the pre industrial conditions the latitudinal distribution of bioclimatic zones suggests that the latitudinal temperature gradient for the langhian would have been significantly shallower than at present and has gradually but asymmetrically become more modern towards the end of the miocene first the southern hemisphere distribution of bioclimatic zones became more modern probably due to the climatic effects of a fully glaciated antarctica the northern hemisphere bioclimatic zone gradient continued to be shallower than modern throughout the miocene and slowly became more modern by the messinian

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

did impacts volcanic eruptions or climate change affect mammalian evolution abstract in recent years it has become popular to attribute faunal change and mass extinction to impacts volcanic eruptions or climatic change how well do these supposed causes compare to the excellent record of cenozoic life especially that of fossil mammals two different cenozoic mammal diversity curves were compared and important climatic volcanic and impact horizons were examined in detail in no case is there a strong correlation between impacts eruptions or climatic events and any episode of mammalian turnover on the contrary most of the known impact eruption and climatic events of the cenozoic occurred during intervals of faunal stability conversely episodes of high turnover and faunal change among cenozoic mammals correlate with no known extrinsic causes apparently extrinsic environmental factors such as impacts eruptions and climate change have a minimal effect and intrinsic biological factors must be more important

paleogene calcite compensation depth in the eastern subtropical pacific answers and questions 1 ocean drilling program leg 199 drilled a north south transect across the eocene paleoequator in the eastern pacific permitting reconstruction the calcite compensation depth ccd since earliest eocene time the ccd was relatively shallow near the early eocene pacific equator 3200 m and unlike modern latitudinal ccd gradients deepened to the north to 3600 m paleolatitude 10 n at 41 ma the ccd underwent a brief sharp transient deepening of 700 m then remained shallow until the eocene oligocene boundary at the e o boundary the ccd deepened by 1200 m in less than 300 kyr this rapid deepening served to more than double the area of seafloor subject to caco3 deposition sea level fall associated with ice volume buildup and ensuing shelf basin fractionation is unlikely to be the sole cause of the increased deep ocean caco3 burial rather a sudden rapid increase in the amount of ca entering the ocean appears necessary to explain the observations

refining the ice flow chronology and subglacial dynamics across the migrating labrador divide of the laurentide ice sheet with age constraints on deglaciation geological survey of canada s geo mapping for energy and minerals ii gem2 program 2013 2020

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

reconstruction of the original extent of the tertiary pre volcanic gravels in the northern sierra nevada ca implications for the range s paleotopography the ancient auriferous gravels that helped spawn the california gold rush have figured prominently in investigations of the cenozoic history of the sierra nevada these fluvial sediments scattered throughout the northern half of the range are the remnants of much larger deposits that accumulated throughout the eocene and early oligocene in this study we present a reconstruction of the original extent of the gravels developed according to a few simple rules this reconstruction suggests that large swaths of the northern sierra nevada were once buried under broad alluvial plains a result consistent with previous work the reconstruction also supports the hypothesis that the gravels accumulated behind high ridges along the sierra nevada foothills with the yuba river providing an important outlet moreover gravel deposits on two high peaks indicate that the gravels may have buried the feather river watershed up to the modern crest of the range finally on the basis of our reconstruction we estimate that the total volume of the gravels was at a minimum 200 km3

equable climates during earth history eocene and cretaceous climate model experiments demonstrate that regardless of conditions of warm polar oceans differences in pole to equator surface temperature gradient or topography above freezing surface temperatures in winter for continental interiors at middle to high latitudes cannot be maintained continental interiors will have cold winter temperatures even during globally warm periods unless currently unrecognized forcing factors influenced past climates if model simulations of eocene and cretaceous climates are accurate the term equable as it applies to paleoclimate should be reconsidered

stable isotopes in large herbivore tooth enamel capture a mid miocene precipitation spike in the interior pacific northwest abstract stable carbon and oxygen isotopes of fossil ungulate tooth enamel were used to investigate the paleoclimate of the pacific northwest from the mid oligocene through pleistocene particularly targeting the mid miocene climatic optimum mmco we specifically test whether precipitation as inferred from tooth enamel 13c values relative to the 13c values of atmospheric co2 13c increased with increasing partial pressure of atmospheric co2 pco2 analysis emphasized water dependent equids rhinos and proboscideans but several artiodactyls and castor were also analyzed as available values of 13c 19 5 in the lower john day 27 and 18 ma and mascall 15 16 ma localities imply relatively high mean annual precipitation map ca 550 800 mm yr values of 13c

tectonic and magmatic evolution of the northwestern basin and range and its transition to unextended volcanic plateaus black rock range nevada the seismically active eastern and western margins of the northern basin and range have been extensively studied yet the northwestern margin of the province remains incompletely understood the black rock range of northwestern nevada straddles the transition from the basin and range province to the south and east and flat lying volcanic plateaus to the west this poorly understood range preserves a remarkably complete record of cenozoic magmatism and provides an important window into the pre miocene history of the unextended volcanic plateaus of northeastern california and southern oregon geologic mapping and 40ar 39ar geochronology from the northern black rock range document three significant episodes of eocene to middle miocene volcanism eocene 35 ma basalts directly overlie mesozoic granites and arc related volcanic and sedimentary rocks locally erupted oligocene to early miocene 27 21 ma bimodal volcanic rocks comprise the bulk of the cenozoic section and conformably overlie the eocene basalt flows these bimodal units include rhyolitic lavas variably welded rhyolitic ash flows unwelded ash fall deposits and thin basalt flows in the neighboring pine forest range 20 km to the north similar oligocene to early miocene units are overlain by more than 500 m of ca 16 4 ma steens equivalent basalt flows and are capped by ca 16 ma rhyolitic ash flow tuffs in the northern black rock range the ca 16 4 ma middle miocene basalts are absent from the section and a 16 2 ma rhyolitic ash flow tuff directly overlies the early miocene flows basaltic and rhyolitic volcanic products in the northern black rock range span 35 16 ma with many of the oligocene volcanic units derived from local vents and dikes despite the map scale complexities of locally derived lava flows the cenozoic section is broadly conformable and dips gently 5 10 to the northwest the region experi enced no significant tilting between 35 and 16 ma with moderate tilting 5 10 and concomitant uplift occurring after 16 ma this tectonic history is consistent with that of the nearby pine forest and santa rosa ranges where low temperature thermochronology documents footwall exhumation along the range bounding normal faults after 12 ma the velocity structure of the crust beneath the northern black rock range is constrained by a recent geophysical survey seismic reflection refraction and gravity and contains gradients that correspond to basin depths predicted by our geologic mapping together with recently completed geological and geophysical studies from the surrounding region our results suggest that the evolution of the northwestern margin of the basin and range was characterized by long lived and voluminous volcanism without significant tectonism followed by low magnitude 20 extension along high angle normal faults

geologic and taphonomic context of el bosque petrificado piedra chamana cajamarca peru abstractvolcanic and volcaniclastic rocks in the northern peruvian andes central caja marca 79 10 w 6 35 s contain a diverse assemblage of permineralized woods known as el bosque petri cado piedra chamana the fossil forest and associated paleosol are preserved in ash fall and lahar deposits of the huambos formation dating of plagio clase from the ash fall deposit using 40 ar 39 ar methods yields a middle eocene age of 39 35 0 21 ma accuracy of this age determination is supported by a more robust sanidine age of 39 52 0 11 ma from an underlying welded ignimbrite fossil wood and leaves associated with the ash fall deposit include vertical trees rooted in the paleosol and buried in situ by the ash fossil wood is also present in high abun dance and diversity in the overlying lahar the fossils are signi cant as a low latitude assem blage including a diversity of both monocots and dicots and in having fossil leaves occur ring in close proximity to fossil woods pre liminary analyses of wood and leaf characters suggest a megathermal climate with some limitations on plant growth associated with limited seasonal moisture availability the assemblage represents lowland tropical forest that was probably growing near sea level and subsequently uplifted to the current elevation at the site 2400 2600 m introduction

age constraints on jerritt canyon and other carlin type gold deposits in the western united states relationship to mid tertiary extension and magmatism carlin type gold deposits are difficult to date and a wide range of ages has been reported for individual deposits therefore several methods were employed to constrain the age of the gold deposits in the jerritt canyon district dated igneous rocks with well documented crosscutting relationships to ore provided the most reliable constraints k ar and 40 ar 39 ar dates on igneous rocks are as follows andesite dikes 324 ma sericitic alteration in andesite dikes 118 ma basalt dikes 40 8 ma quartz monzonite dikes 39 2 ma and calc alkaline ignimbrites 43 1 to 40 1 ma of these only the andesite and basalt dikes are clearly altered and mineralized the gold deposits are therefore younger than the 40 8 ma basalt dikes the sericitic alteration in the andesite dikes is unrelated to the gold deposits a number of dating techniques did not work k ar and 40 ar 39 ar dates on mica from mineralized ordovician to devonian sedimentary rocks gave misleading results the youngest date of 149 ma from the smallest 187 os 188 os initial 0 9 3 6 but did not yield a meaningful isochron due to very low re and os concentrations and large analytical uncertainties paleomagnetic dating techniques failed because the hydrothermal fluids sulfidized nearly all of the iron in the host rocks leaving no remnant magnetism when published isotopic dates from other carlin type deposits in nevada and utah are subject to the rigorous evaluation developed for the jerritt canyon study most deposits can be shown to have formed between 42 and 30 ma k ar and 40 ar 39 ar dates on the youngest preore igneous rocks range from 41 to 32 ma whereas the oldest postore igneous rocks range from 35 to 33 ma hydrothermal adularia from the twin creeks deposit yields similar 40 ar 39 ar dates of 42 ma k ar dates on supergene alunite range from 4 to 30 ma k ar and 40 ar 39 ar dates on micas separated from sedimentary 395 43 ma and igneous 145 38 ma rocks are usually much older than the gold deposits and most are suspect because they are from incompletely reset preore micas or from mixtures of preore and ore stage mica fission track dates on zircons are also generally older than the deposits 169 35 ma and are not completely reset by mineralization apatites are likley to be reset by the hydrothermal systems and by younger thermal events and yield dates 83 22 ma that are younger than those from zircon independent support of a mid tertiary age is provided by the low delta d sub h 2 o values of hydrothermal fluids from 10 widely separated carlin type deposits 134 or 23ppm the low delta d sub h 2 o values are consistent with a mid tertiary age when the climate was cool but are inconsistent with the cretaceous and jurassic ages favored by some workers when the climate was warm the age and distribution of carlin type deposits coincides with areas that underwent extension and calc alkaline magmatism over the same time period despite this relationship the deposits lack clear spatial or genetic relationships to mid tertiary epizonal plutons rather many deposits are localized along preexisting crustal fault zones in the getchell trend structures tapped deep sourced metamorphic or magmatic fluids and subsequently variably exchanged meteoric water in the other trends and districts only variably exchanged meteoric water has been detected these relationships suggest either that all of the deposits formed from deep sourced fluids and were subsequently flooded by meteoric water or that fluids from different sources evolved to produce deposits with similar charateristics

a methodology for targeting palaeo proxy data acquisition a case study for the terrestrial late miocene when planning the acquisition of new palaeo proxy data for reconstructing past climates many factors influence the decision of where the proxies are to be collected one such influence is the likelihood of recording a significant climate change relative to the modern another consideration which is less often considered is the desire to target regions in which there is significant uncertainty in numerical model predictions of past climate change new proxy data in these regions enables a more rigorous test of model simulations and results in better constraints on the various boundary conditions used to force the models in this paper we present a methodology for targeting new palaeo proxy data based on model simulations we use the terrestrial late miocene 11 6 to 5 3 ma as a case study the late miocene climate provides insights into future climate behavior as it is believed to have been considerably warmer than the modern we carry out a suite of late miocene atmosphere only general circulation model simulations which we initially evaluate relative to an example dataset of terrestrial temperature and precipitation in terms of targeting future data acquisition we locate those regions in the model which exhibit the largest change in temperature and or precipitation relative to the pre industrial we also locate those regions which display the largest variability between the model simulations because new data in these regions are most likely to provide a strict test of the reliability of the model results among other regions the amazon basin the chad basin central canada and northern india are identified as potentially useful areas to collect data

eocene circulation of the southern ocean was antarctica kept warm by subtropical waters 1 near the eocene s close 34 million years ago the climate system underwent one of the largest shifts in earth s history antarctic terrestrial ice sheets suddenly grew and ocean productivity patterns changed previous studies conjectured that poleward penetration of warm subtropical currents the east australian current eac in particular caused eocene antarctic warmth late eocene opening of an ocean gateway between australia and antarctica was conjectured to have disrupted the eac cooled antarctica and allowed ice sheets to develop here we reconstruct eocene paleoceanographic circulation in the tasmanian region using 1 biogeographical distributions of phytoplankton including data from recently drilled ocean drilling program leg 189 sites and 2 fully coupled climate model simulations we find that the eac did not penetrate to high latitudes and ocean heat transport in the region was not greater than modern our results do not support changes in thermal isolation as the primary driver of the eocene oligocene climatic transition

oxygen isotope evidence for the late cenozoic development of an orographic rain shadow in eastern washington usa topographic development of the southern washington cascade range and its influence on regional climate on the leeward side of the range for the past 15 6 m y are evaluated using oxygen isotope ratios d 18 o of ancient meteoric water recorded in authigenic smec tites the d 18 o values of authigenic smectites from paleosols and altered tuffs on the east side of the range exhibit a temporal and continuous decrease of 3 4 from 15 6 ma to the present taking into account a regional temperature change in eastern washington since the middle miocene the calculated d 18 o values of regional meteoric water show a negative shift of 3 5 4 5 over the same interval such a decrease is similar to the change in the d 18 o values of modern precipitation from the coastal side to a region down wind of the washington cascades this negative shift of the calculated d 18 o values on the east side of the range is best explained by the development of a rain shadow due to the tectonic rock uplift of the cascades during the late cenozoic based on the empirically calculated relationship between change in elevation and change in the d 18 o value of pre cipitation paleorelief of the southern washington cascades since 15 6 ma is estimated to be 1 2 1 7 km

fossil biotas from the okanagan highlands southern british columbia and northeastern washington state climates and ecosystems across an eocene landscape the late early to early middle eocene okanagan highlands fossil sites spanning 1000 km north south northeastern washington state southern british columbia provide an opportunity to reconstruct biotic communities across a broad upland landscape during the warmest part of the cenozoic plant taxa from these fossil sites are characteristic of the modern eastern north american deciduous forest zone principally the mixed mesophytic forest but also include extinct taxa taxa known only from eastern asian mesothermal forests and a small number of taxa restricted to the present day north american west coast coniferous biome in this preliminary report paleoclimates and forest types are reconstructed using collections from republic in washington state usa and princeton quilchena falkland mcabee hat creek horsefly and driftwood canyon in british columbia canada both leaf margin analysis lma and quantitative bioclimatic analysis of identified nearest living relatives of megaflora indicated uppe

paleovalley morphology and fluvial system evolution of eocene oligocene sediments auriferous gravels northern sierra nevada california implications for climate tectonics and topography in the northern sierra nevada california eocene oligocene fluvial sediments the auriferous gravels rest unconformably in well defined basement incised paleovalleys providing a record of paleolandscape geomorphology and drainage system evolution paleovalley surface mapping shows that local topography and bedrock lithology controlled the location of broad terraced paleovalley segments which formed in the central and eastern metamorphic bedrock belts and subsequently became areas of significant fluvial deposition high gradient high energy deposits are present near the edges of these areas suggesting that tributaries and outlets resided in steeper narrow paleovalleys multiple strath terraces are common in broad paleovalleys indicating that incision events occurred both before deposition and during paleovalley widening followed by periods of aggradation broad paleovalley deposits contain predominantly braided stream facies deposited in an energetically variable system multiple upward fining cycles bounded by erosional surfaces are composed of alternating coarse grained channel belt and fine grained floodplain packages an overall upward fining succession suggests that the locus of fluvial deposition shifted and depositional energy waned over time as the system backfilled successive broad paleovalleys paleochannel slope estimates of 0 004 0 055 were obtained based on average grain sizes of coarse channel fills anomalously thick up to 11 m laterally continuous 1 3 km floodplain units containing kaolinite rich clay and oxisol intervals record high fine grained sediment supply driven by high rates of chemical weathering in the warm eocene climate based on sedimentary characteristics combined with floral and detrital zircon data braided stream deposition within the basin occurred from the late early eocene through late eocene and aggradation primarily occurred in broad lower gradient reaches behind a major bedrock knickpoint created in the late mesozoic early cenozoic possibly due to asymmetric batholith unroofing the diachronous localized nature of paleovalley incision and braided stream aggradation within the northern sierra nevada invalidates previous estimates of the timing and amount of range uplift based on paleochannel reconstructions and gradients both internal and external drivers influenced the evolution of the fluvial system through 1 the pattern of basin filling as the locus of deposition migrated east to west 2 the warm eocene climate which increased chemical weathering and contributed a high sediment supply and 3 changes in base level due to eustasy and or laramide tectonism this record of laramide tectonics in the sierra nevada and basin and range is important for the timing of sierra nevada uplift for tectonic reconstructions of western north america and for studies of landscape evolution in tectonically active orogens

a late miocene subtropical dry flora from the northern altiplano bolivia abstract a variety of evidence suggests that the altiplano of the central andes the second highest and largest plateau on earth underwent significant uplift in the late miocene pliocene the most important datum supporting recent uplift is a collection of the 10 66 0 06 ma jakokkota flora from west central bolivia which implies a paleoelevation no more than 1600 1200 m today the site has an elevation of almost 4000 m in order to test the reliability of this estimate the present study analyzes a new collection of the jakokkota flora from a lacustrine unit that is 0 2 0 5 myr younger than the previously analyzed collection from a fluvial unit climate estimates based on leaf morphology for the two collections are statistically indistinguishable the combined flora has a mean annual temperature of 21 5 2 0 c and a mean annual precipitation of 550 180 mm the similarity of the climate estimates for the two floras suggests that there was not a significant climate change between them nor a significant bias in the leaf morphology due to differing taphonomic processes the climate estimate for the combined flora thus presents a representative picture of the late miocene climate of the northern altiplano if one assumes that the climate of the tropics has not changed significantly since the late miocene as is suggested by marine isotopic data then the paleoclimate of the jakokkota flora implies a paleoelevation of 1160 600 m thus the jakokkota flora supports the hypothesis of a young age for the altiplano

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

early eocene ypresian birds from the okanagan highlands british columbia canada and washington state usa we survey the known avian fossils from ypresian early eocene fossil sites of the north american okanagan highlands mainly in british columbia canada all specimens represent taxa that were pre

north american nonmarine climates and vegetation during the late cretaceous abstract analyses of physiognomy of late cretaceous leaf assemblages and of structural adaptations of late cretaceous dicotyledonous woods indicate that megathermal vegetation was an open canopy broad leaved evergreen woodland that existed under low to moderate amounts of rainfall evenly distributed through the year with a moderate increase at about 40 45 n many dicotyledons were probably large massive trees but the tallest trees were evergreen conifers megathermal climate extended up to paleolatitude 45 50 n mesothermal vegetation was at least partially an open broad leaved evergreen woodland perhaps a mosaic of woodland and forest but the evapotranspirational stress was less than in megathermal climate some dicotyledons were large trees but most were shrubs or small trees evergreen conifers were the major tree element some mild seasonality is evidenced in mesothermal woods precipitational levels probably varied markedly from year to year northward of approximately paleolatitude 65 n evergreen vegetation was replaced by predominantly deciduous vegetation this replacement is presumably related primarily to seasonality of light the southern part of the deciduous vegetation probably existed under mesothermal climate comparisons to leaf and wood assemblages from other continents are generally consistent with the vegetational climatic patterns suggested from north american data limited data from equatorial regions suggest low rainfall late cretaceous climates except probably those of the cenomanian had only moderate change through time temperatures generally appear to have warmed into the santonian cooled slightly into the campanian and more markedly into the maastrichtian and then returned to santonian values by the late maastrichtian the early eocene was probably warmer than any period of the late cretaceous latitudinal temperature gradients were lower than at present for the campanian and maastrichtian a gradient of about 0 3 c 1 latitude is inferred equability was high a mean annual range of temperature of about 8 c is inferred for paleolatitude 51 56 n during the campanian most late cretaceous plants evolved in a climate characterized by absence of freezing and low to moderate amounts of precipitation a brief low temperature excursion and a major long lasting increase in precipitation occurred at the cretaceous tertiary boundary in megathermal climates these events selected for plants that could exist in rainforest environments in mesothermal climates deciduousness and contamitant structural adaptations were selected the events at the cretaceous tertiary boundary had a major and long lasting impact on the evolution of land plants and their ecosystems low precipitation at low to middle late cretaceous latitudes is suggested to be the result of high levels of atmospheric co2 which in turn are probably related to inability of warm saline oceans to store large amounts of carbon conditions appear to have rapidly changed at the cretaceous tertiary boundary when oceanic circulation and stratification may have been fundamentally altered after the boundary the oceans were apparently able to store much greater amounts of carbon and the oceans withdrew large amounts of co2 from the atmosphere in turn more precipitation fell at low to middle latitudes the resulting high biomass vegetation formed a second major carbon reservoir to keep atmospheric co2 low relative to the late cretaceous changes in oceanic and atmospheric circulation probably resulted from some factor external to the ocean atmosphere system

late miocene climate and life on land in oregon within a context of neogene global change abstract clarendonian 12 ma fossil soils plants molluscs fish and mammals of eastern oregon allow reconstruction of late miocene paleogeography paleoclimate and paleoecology on land between the global thermal maximum of the middle miocene 16 ma and global cooling and drying of the late miocene 7 ma six different pedotypes of paleosols recognized near unity and juntura allow reinterpretation of local mammalian paleoecology fossil beavers dominated gleyed entisols of riparian forest abundant camels and common hipparionine horses dominated alfisols of wooded grassland and grassy woodland diatomites overlying mammal bearing beds have bullhead catfish ictalurus ameiurus vespertinus as well as fossil leaves dominated by live oak quercus pollardiana fossil plants and soils of unity and juntura are most like those of grassy live oak woodland and savanna on the western slopes of the sierra nevada in northern california today fossil plants and soils indicate mean annual temperature of 12 9 7 7 17 7 c and mean annual precipitation of 879 604 1098 mm miocene paleoclimatic changes in eastern oregon show no relationship to changes in oxygen isotopic composition of marine foraminifera usually taken as an index of global paleoclimatic change mismatch between land and sea paleoclimatic records is most likely an artefact of global ice volume perturbation of oxygen isotopic values instead miocene paleoclimatic change in eastern oregon parallels changes in carbon isotopic composition of marine foraminifera presumably through fluctuations in greenhouse gases

spatial and temporal variation of cenozoic surface elevation in the great basin and sierra nevada the surface uplift of mountain belts caused by tectonism plays an important role in determining the long term climate evolution of the earth however the general lack of information on the paleotopography of mountain belts limits our ability to identify the links and feedbacks between topography tectonics and climate change on geologic time scales here we present a 1 8 o and d record of authigenic minerals for the northern great basin that captures the timing and magnitude of regional surface uplift and subsidence events in the western united states during the cenozoic authigenic calcite smectite and chert 1 8 o values suggest the northern great basin region experienced 2km of surface uplift between the middle eocene and early oligocene followed by 1 to 2km of surface subsidence in the southern great basin and or sierra nevada since the middle miocene these data when combined with previously published work show that the surface uplift history varied in both space and time surface uplift migrated from north to south with high elevations in southern british columbia and northeastern washington in the middle eocene and development of surface uplift in north and central nevada in the oligocene this pattern of north to south surface uplift is similar to the timing of magmatism in the western cordillera a result that supports tectonic models linking magamtism with removal of mantle lithosphere and or a subducting slab

synorogenic evolution of large scale drainage patterns isotope paleohydrology of sequential laramide basins in the past decade we and others have compiled an extensive dataset of o c and sr isotope stratigraphies from sedimentary basins throughout the paleogene north american cordillera in this study we present new results from the piceance creek basin of northwest colorado which record the evolving hydrology of the eocene green river lake system we then place the new data in the context of the broader cordilleran dataset and summarize implications for understanding the synorogenic evolution of large scale drainage patterns the combined data reflect 1 a period of throughgoing foreland rivers heading in the sevier fold and thrust belt and flowing east 2 ponding of freshwater lakes in the foredeep as laramide uplifts blocked drainage 3 hydrologic closure that led to both intensive evaporation in the terminal sink of the piceance creek basin and integration of catchments over length scales 1000 km 4 infilling of basin accommodation by southward migrating magmatism in distal catchments leading to the freshening and demise of intraforeland lakes that also stepped south over time

paleoenvironmental reconstruction of a middle miocene forest from the western canadian arctic abstract abundant fossil plant remains are preserved in deposits of middle miocene age of the ballast brook formation on banks island northwest territories canada intact seed cones logs and stumps are preserved in situ as mummified remains and present an opportunity to reconstruct the composition structure and productivity of a pinaceae dominated forest that once grew north of the arctic circle paleolatitude ca 74 n we mapped and measured 78 tree stumps exposed in three dimensions on a 0 12 ha peat layer an analysis of the wood anatomy and seed cones indicates that a haploxylon pine dominated this lowland forest although species of both picea and glyptostrobus were growing in the swamp as well stump diameters ranged from 7 cm to 108 cm average 42 cm we utilized allometric relationships to predict tree heights based on the stump diameters in the fossil forest our results indicate that the average tree height of this miocene forest may have been as large as 21 m we used stump diameter data and predicted tree height to calculate the parabolic stem volume and stem biomass for the exposed area of fossil forest stem biomass assuming an average wood density of 410 kg m 3 may have been as great as 259 mg ha 1 or as little at 202 mg ha 1 the annual ring width of the stem wood sampled in the field was 1 26 mm for pinus 1 20 mm for picea and 0 21 mm for glyptostrobus based on these growth rates our estimate of biomass sequestered aboveground as wood is at most 3 8 mg ha 1 y 1 based on our estimates these lowland forest communities were of moderate biomass and productivity typical of modern cool temperate forests in north america

oxygen isotope evidence for progressive uplift of the cascade range oregon oxygen isotope compositions of fossil equid teeth in the cascade rainshadow reveal a v5x decrease in mean n 18 o since 27 ma isotopic changes are inconsistent with expected effects from global climate change because a the expected isotopic shift to tooth n 18 o values due to global climate change v1x is much smaller than the observed shift b predicted and observed isotopic trends are opposite for oligocene vs miocene samples and c average compositions and ranges in compositions remained unchanged for samples from before and after major global cooling in the mid miocene accounting for a decrease in relative humidity of at least 15 we infer a topographically driven secular shift in the n 18 o value of rainwater of 6 8x since the late oligocene which is approximately equivalent to the modern day difference in n 18 o values of precipitation and surface waters across the central cascades rise of the central cascades apparently occurred monotonically over the last 27 ma with a hiatus between v15 4 and 7 2 ma possibly related to eruption of the columbia river basalts progressive volcanic accumulation over tens of millions of years best explains the data rather than a short lived uplift event paleoseasonality as inferred from isotope zoning and intertooth variability decreased dramatically from 7 9x at 15 4 7 ma to v3x at 3 ma then increased to 6 8x today the cause of the decrease in seasonality at 3 ma may reflect either brief warming during the mid pliocene within the context of global tectonic reorganization or consumption by equids of water from an isotopically buffered lake idaho 2002 elsevier science b v all rights reserved

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

cenozoic paleoclimate on land in north america abstract paleotemperature and paleoprecipitation over the past 40 m yr can be inferred from the degree of chemical weathering and depth of carbonate nodules in paleosols of oregon montana and nebraska paleosol records show that late eocene 35 ma middle miocene 16 ma late miocene 7 ma and early pliocene 4 ma warm climatic episodes were also times of a wet climate in oregon montana and nebraska oregon and nebraska were humid during warm wet times but montana was no wetter than subhumid within the rain shadow of intermontane basins global warm wet paleoclimatic spikes steepened rather than flattened geographic gradients of rocky mountain rain shadows long lived mountain barriers created dusty dry basins with sedimentation rates high enough to preserve milankovitch scale 100 41 kyr global paleoclimatic variation in some sequences of paleosols greenhouse warm wet climates indicated by paleosols were also peaks of diversity for north american plants and animals and coincided with advance

radiometric dating of ash partings in coal of the eocene puget group washington implications for paleobotanical stages new 40 k 40 ar and fission track ages from volcanic ash partings in coal beds of the eocene puget group of western washington indicate a time span of about 41 2 1 8 to 45 0 2 1 2 m y for the 1 890 m section of sediments exposed in the green river area these age data do not entirely support the previous early eocene through early oligocene paleobotanical age estimates for this section and for the four paleobotanical stages defined within it radiometric dating of floras assigned to the same stages outside the type section appears to be partially inconsistent with radiometric ages from the type section

tertiary climatic changes at middle latitudes of western north america abstract a new multivariate analysis of leaf physiognomy provides the basis for estimating various climatic parameters for angiosperm leaf assemblages estimates from this climate leaf analysis multivariate program clamp are both accurate valid and precise repeatable application of clamp to fossil leaf assemblages from western north america confirms that eocene mean annual temperature mat was generally high early eocene mat 19 c at paleolat 70 n and 27 c at paleolat 45 n significant fluctuations 5 8 in mat occurred during the eocene each successive warm period was cooler than the preceding warm period mean annual range of temperature mart was generally low during the eocene especially at middle latitudes but then markedly increased by 12 13 c at 33 ma as mat decreased by 7 8 c these changes at 33 ma largely involved a decrease in cold month mean temperature which continued to decline into the early miocene but then increased significantly into the mid miocene thermal optimum warm month mean temperature changed little from the eocene through the early miocene this parameter however markedly decreased at 13 ma which coincides with the growth of the east antarctic ice sheet clamp also indicates that the coastal region of western north america had significantly higher mat than interior regions such as the great basin and rocky mountains these differences in mat appeared by or during the eocene and indicate that much of the interior had high altitudes in the paleogene these inferences have a significant bearing on global circulation models proposed for tertiary climates

from the semiarid landscapes of southwestern usa to the wet tropical zone of southeastern brazil reflections on the development of cuestas pediments and talus abstract classical geomorphological models consider that escarpment retreat of cuesta landforms is fastest in arid and semiarid regions which would be expected to lead to increased talus production however this is in disagreement with the piedmont zone of the colorado plateau cliffs arid semiarid region of southwestern usa where talus is as inconspicuous as the deposits of the cuesta escarpment footslopes of the parana basin wet tropical region of southeastern brazil thus this paper discusses the evolutionary processes of cuesta escarpments pediments and piedmont deposits in both wet tropical regions and arid zones considering the key areas of the serra geral ridge in the parana basin and the eastern central colorado plateau as examples this manuscript constitutes a comprehensive and critical review of the principal literature on the landform development of such regions research has revealed that despite the production of sediment fine coarse from the escarpments in the arid southwestern usa geochemical weathering and freeze thaw cycles quickly destroy talus deposits furthermore chemical weathering dissolves minerals and forms caverns within the rock walls of mesas and in amphitheaters and canyons influencing escarpment retreat directly despite mechanical processes being the most important factors controlling landform development on the other hand in regions characterized by the wet tropical climate of brazil geochemical processes are more intense and they destroy the talus very quickly enhancing deep weathering however mechanical morphogenesis is also frequent in such regions forming in deforested areas features very similar to those found in the badlands of dry zones chemical and physical mechanical processes have very different intensities in dry arid and wet tropical areas but these processes are very relevant to landform development in both environments the rates of escarpment retreat are higher in the dry areas of the colorado plateau than estimated for the brazilian tropical zones which is in accordance with classical models these variations are probably related not only to climate but also to lithological differences the tops of the mesas on the colorado plateau are supported by thin strongly cemented conglomeratic fluvial sandstones whereas the caprocks of the brazilian cuesta landforms comprise thick basalt flows capped by ferruginous cuirasses in some cases lithological characteristics are more important than climate regarding escarpment retreat

early eocene biotic and climatic change in interior western north america imprecise correlation of the marine and terrestrial fossil records has been a major obstacle to understanding migration and extinction of continental biotas and early cenozoic climate change new sup 40 ar sup 39 ar data from the willwood formation in the bighorn basin of wyoming establish an age of 52 8 plus minus 0 3 ma for earliest lostcabinian late wasatchian faunas and coeval early eocene floras strata just beneath earliest wasatchian faunas can be correlated with the np9 np10 boundary in marine sedimentary units which has an interpolated age of approximately 55 7 ma this new information allows the authors to estimate the durations of the wasatchian approximately 5 m y and the lostcabinian approximately 2 m y and shows that the continental biotas are coeval with the acme of cenozoic warmth inferred from delta sup 18 o measurements of foraminifera from 58 to 50 ma paleoclimate in the continental interior at about 45 degree n was warm and equable but patterns of temperature change inferred from continental floras do not track precisely the marine delta sup 18 o record

middle to late cenozoic cooling and high topography in the central rocky mountains constraints from clumped isotope geochemistry abstract the timing and mechanism of the formation of the high elevations of the central rocky mountains rockies in the western interior of north america remain controversial we examine the middle and late cenozoic paleorelief between the great plains and the central rockies using clumped isotope geothermometry of carbonate cements of fluvial and eolian sandstones our petrographic observations suggest that the studied carbonate cements were formed primarily during eodiagenesis in near surface conditions and retain primary paleoclimate and paleoelevation signals carbonate clumped isotope temperatures decrease 10 c and calculated water o 18 values decrease 4 from 35 ma to 5 ma in both the central rockies and the western great plains following middle and late cenozoic global cooling trend a persistent longitudinal gradient in temperature and o 18 value existed between the central rockies and the great plains during the oligocene and miocene with temperatures 4 8 c higher and calculated water o 18 values 3 6 higher in the great plains these observations suggest the mean elevation of the central rockies was 1 km higher than the western great plains during the middle and late cenozoic similar to the present day regional relief when placed in the context of other paleoaltimetry studies and geological observations our findings support the hypothesis that the high mean topography of the rockies was developed during the late eocene possibly related to isostatic adjustment or dynamic uplift caused by foundering of lower mantle lithosphere or the farallon slab or both

neogene aridification of the northern hemisphere neogene cooling and aridification in the northern hemisphere have long been recognized but there are no studies comparing patterns of aridity gradients or differences between north america and eurasia large herbivorous mammals are an excellent source for understanding large scale environmental and climatic patterns because their molar crown height hypsodonty reflects both habitat and precipitation the temporal development of hypsodonty in the north american great plains is well studied but both spatial detail and comparisons with patterns in eurasia are lacking here we use a methodology based on community levels of hypsodonty to estimate precipitation during the neogene the past 23 ma we show that aridification was more profound and occurred 5 ma earlier in north america than in eurasia by combining our results with existing climate model output and new sensitivity experiments we show how these changes were influenced by ocean heat transport and atmospheric circulation patterns we further suggest that asymmetric dispersal of large mammals between eurasia and north america was related to the contrasting humidity regimes between the continents

faunal stability during the early oligocene climatic crash abstract traditional neo darwinism views species as highly flexible entities which adapt to climatic change by gradually evolving new morphologies of the 177 species of mammals from the upper eocene lower oligocene 37 30 ma white river group in the high plains most species are static for 2 4 million years on average and some persist much longer only three examples of gradualism can be documented in the entire fauna and these are mostly size changes contrary to expectations most mammalian species show no change during the earliest oligocene climatic crash 33 2 ma in spite of the fact that the vegetation changed from dense forests to open forested grassland mean annual temperatures dropped 13 c and conditions got much drier and more seasonal only a few mammalian lineages speciated a few more went extinct and the vast majority 62 out of 70 persisted through this climatic event with no observable response whatsoever this evidence shows that organisms are much less responsive to the environment than short term neontological studies suggest

a late miocene climate model simulation with echam4 ml and its quantitative validation with terrestrial proxy data abstract for the tortonian late miocene 11 to 7 ma we present a model simulation using the atmospheric general circulation model agcm echam4 coupled to a mixed layer ml ocean model the tortonian simulation with echam4 ml includes an adjusted weaker than present ocean heat transport a generally lower palaeorography and an appropriate palaeovegetation we analyse the climatic differences between the tortonian run and the present day control experiment and we validate our tortonian model results for the mean annual temperature and the annual precipitation with quantitative terrestrial proxy data globally the tortonian run is slightly warmer 0 6 c and the global precipitation indicates more humid conditions 27 mm a than the pd control run particularly the northern high latitudes are warmer 3 5 c in the tortonian simulation which leads to a weaker meridional temperature gradient than today as well as to a reduction of polar sea ice we attribute the polar warming to the lowering of the greenland elevation 20 c in the miocene and to the effects of the palaeovegetation the reduced altitude of the tibetan plateau causes a warming 20 c as compared to today and leads to a weaker asian monsoon in the tortonian run for europe the mean annual temperature is almost unaffected as compared to today because a cooling effect of the weak palaeocean heat transport is compensated by the palaeovegetation when validating our model results we find that the tortonian run is largely consistent with quantitative proxy data however the high latitudes tend to be generally too cool in the palaeoclimate simulation and the equator to pole temperature gradient is too steep as compared to proxy data for europe the comparison with proxy data indicates that the tortonian simulation underestimates the mean annual temperatures but precipitation patterns are quite consistent between model results and proxy data overall the tortonian run is quite realistic and hence the model simulation contributes to a better understanding of the relevant climate processes in the miocene however the discrepancies to proxy data demonstrate that we still do not sufficiently understand the late miocene climate

ocean and climate response to north atlantic seaway changes at the onset of long term eocene cooling abstract around the early middle eocene boundary the first occurrence of contourite drift sediments and widespread deep ocean erosion indicate changes in the north atlantic ocean circulation interestingly these changes coincide with the first steps of cenozoic cooling from the paleogene greenhouse climate towards the modern icehouse the cause for this ocean circulation reorganization is poorly understood since modern water mass tracers may have worked fundamentally different in the past and the paleoceanographic proxy record is limited in both time and space as a result it is challenging to reliably reconstruct the climatic and tectonic boundary conditions e g atmospheric greenhouse gas concentration and the depth and geometry of developing and closing passages between ocean basins in this study we attempt to identify thresholds in tectonic gateway passages and atmospheric co2 concentration using the fully coupled earth system model cosmos indeed the simulation of earth s past climates can unravel the physical processes driving deep water formation in a greenhouse world specifically we use cosmos to evaluate the impact of changes in the north atlantic gateways at the early middle eocene boundary on the north atlantic deep western boundary currents under low obliquity configuration we find that northern component waters start to form when the greenland scotland ridge reaches a threshold depth of deeper than 200 m while the arctic ocean is still shut off from the north atlantic in this scenario the relatively deep greenland scotland ridge allows for sufficient inflow of warm salty atlantic surface waters into the nordic seas to initiate convection during winter cooling opening the seaway towards the arctic leads to a cessation of northern component water formation as it allows for inflow of brackish surface waters into the northern nordic seas hindering northern component water formation

formation history and physical properties of sediments from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract the synthesis of available geological information and surface temperature evolution in the alaska north slope region suggests that biogenic and deeper thermogenic gases migrated through fault networks and preferentially invaded coarse grained layers that have relatively high hydraulic conductivity and low gas entry pressures hydrate started forming before the beginning of the permafrost eventually the permafrost deepened and any remaining free water froze so that ice and hydrate may coexist at some elevations the single tested specimen depth 620 47 620 62 m from the d unit consists of uncemented quartzitic fine sand with a high fraction of fines 56 by mass finer than sieve 200 the as received specimen shows no evidence of gas present the surface texture of sediment grains is compatible with a fluvial deltaic sedimentation environment and shows no signs of glacial entrainment tests conducted on sediments with and without thf hydrates show that effective stress porosity and hydrate saturation are the major controls on the mechanical and geophysical properties previously derived relationships between these variables and mechanical geophysical parameters properly fit the measurements gathered with mount elbert specimens at different hydrate saturations and effective stress levels we show that these measurements can be combined with index properties and empirical geomechanical relationships to estimate engineering design parameters volumetric strains measured during hydrate dissociation vanish at 2 4 mpa therefore minimal volumetric strains are anticipated during gas production at the mount elbert well however volume changes could increase if extensive grain crushing takes place during depressurization driven production strategies if the sediment has unexpectedly high in situ porosity associated to the formation history or if fines migration and clogging cause a situation of sustained sand production

testing the climatic estimates from different palaeobotanical methods an example from the middle miocene shanwang flora of china the miocene shanwang biota from eastern china contains exceptionally well preserved plant fossils with abundant leaf fossils and palynomorphs co occurring at several levels in the sedimentary succession this has provided an ideal opportunity to undertake detailed comparative quantitative palaeoclimate reconstruction based on both mega and microfloral assemblages using various approaches namely the coexistence approach coa leaf margin analysis lma and climate leaf analysis multivariate programme clamp by applying these approaches to the same dataset and using multiple fossil assemblages from different levels we are able to compare results from the different methods of climate prediction clamp and lma give consistently lower temperature mean annual temperature mat predictions than the coa taking errors into account all methods indicate no overall climate change through the sequence studied results from coa show overall agreement in the palaeoclimate parameters obtained using both pollen and leaf datasets indicating a high degree of internal consistency with this method

stable isotope records of hydrologic change and paleotemperature from smectite in cenozoic western north america abstract the oxygen and hydrogen isotopic composition of soil water 18ow and dw hereafter reflect the history of water through processes such as source evaporation precipitation and vapor recycling temperature humidity evaporation and post condensation processes can affect 18ow and dw as such isotope proxy records are often limited in their ability to constrain paleoclimate paleoecology or paleoelevation without independently corroborating data smectite preserves both the hydrogen and oxygen isotope signature of parent water and therefore provides critical insight into meteoric water line relationships and paleotemperature here we use in situ pedogenic smectite 18o and d records to characterize the evolution of the hydrologic cycle in cenozoic western north america we incorporate 192 samples 119 of which are previously unpublished from 11 cenozoic basins representing a range of environments in the basin and range rocky mountains and great plains our results indicate that the processes controlling smectite isotopic compositions vary both regionally and temporally in some localities such as oligocene to pleistocene western nebraska change in temperature is the primary control on smectite isotopic composition in other basins such as in miocene trapper creek id isotope values lie along the meteoric water line suggesting change in meteoric water composition is responsible for the variation in most basins especially those in the neogene basin and range smectite line slope suggests either evaporation of previously meteoric water or a combination of change in paleotemperature and meteoric water composition smectite geothermometry suggests mineral formation temperatures of 30 40 c in the middle miocene in the rocky mountains great plains and basin and range and a decrease of 10 15 c since the middle miocene climatic optimum consistent with clumped isotope and paleofloral temperature estimates

possible regional tectonic controls on mammalian evolution in western north america abstract previous work has suggested that tectonically active regions act as speciation pumps for mammals and plant species but little is known about how fast or widespread tectonism must be in order to directly influence evolution here we use oxygen and hydrogen isotopic data from miocene sedimentary deposits to characterize the topographic evolution of the southern columbia plateau snake river plain and northern rocky mountain regions during the yellowstone hotspot passage with the ultimate goal of understanding whether topographic changes caused by the hotspot influenced mammalian evolution within those regions we conducted oxygen isotope analyses of 130 samples of lacustrine and paleosol carbonate from miocene stratigraphic sections that span much of the northern rocky mountain region and combined these data with previously published isotopic records collectively these isotopic data show that caldera formation associated with the yellowstone hotspot has modified regional topography and rearranged drainages along the track of the hotspot and that the hotspot has left a topographic depression in its wake we explore the extent to which these topographic changes influenced or are decoupled from diversity changes exhibited by the local mammal faunas and conclude that the passage of the hotspot and consequent surface uplift created rainshadows in the lee of high elevation calderas and or generated large volumes of volcanic materials influencing soils and vegetation collectively that may explain a possible rise in mammal diversity in the cp srp region at 14 ma coincident with a drop in diversity in the nrm it is still unclear however how different taphonomic pathways and sample standardization problems are influencing apparent diversity peaks at this temporal and geographic resolution

are two elements better than one dual isotope ratio detrending of evaporative effects on lake carbonate paleoelevation proxies 1 stable isotope based proxy methods enhance our ability to interpret geodynamical histories for tectonic provinces via paleoelevational reconstructions these methods require that the unmodified isotopic composition of meteoric water is recorded by authigenic minerals a critical assumption that has not been tested across wide ranging environmental and topographical contexts here we show that quaternary lake carbonate 18o values are not strongly nor significantly correlated with regional elevation due to the isotopic modification of in flow waters following entry into the lake environment these modifications are largely caused by surface water evaporation and can result in 3 km errors in paleoelevation estimates if not accounted for however our analysis suggests that positive shifts in surface water 18o are accompanied by similar magnitude shifts in 13c dic this positive co variation in 18o and 13c may be used to detrend lake carbonate compositions for the effects of surface water evaporation using a parameter we define here as the 13c excess when tibetan lakes are excluded from the data set 13c excess values are significantly correlated with mean up slope hypsometric altitude with an error of 500 m application of the13c excess approach to cenozoic lake carbonate records from the western u s cordillera both challenges and reinforces previous paleoelevational interpretations based on 18o alone

alteration of the callovo oxfordian clay from meuse haute marne underground laboratory france by alkaline solution ii modelling of mineral reactions abstract one of the french options for the final disposal of high level radioactive waste is a deep geological repository the callovo oxfordian formation in the meuse and haute marne france was proposed by the french agency for the management of radioactive wastes andra to be the site of a research laboratory in order to evaluate in situ the interaction between the host formation and the engineered barriers in the previous experimental part secondary minerals such as zeolites tobermorite and katoite have been observed after the alteration of the callovo oxfordian clay under alkaline conditions three different reactions of phyllosilicates alteration have been proposed as a function of both ph and chemical composition of the reacting solutions the aim of this work was to simulate the reaction between the callovo oxfordian clay and high ph solutions in order to validate the proposed alteration reactions from experimental data the thermodynamic modelling of stability relationships among minerals in the callovo oxfordian clay was performed using the solution speciation solubility modelling code kindis at 120 c for different chemical media naoh koh and ca oh 2 input data were the mineralogical composition of the

sensitivity of seawater oxygen isotopes to climatic and tectonic boundary conditions in an early paleogene simulation with giss modele r 1 an isotope enabled ocean atmosphere general circulation model giss modele r is used to estimate the spatial gradients of the oxygen isotopic composition of seawater 18osw where is the deviation from a known reference material in per mil during the early paleogene 45 65 ma understanding the response of 18osw to changes in climatic and tectonic boundary conditions is important because records of carbonate 18o document changes in hydrology as well as changes in temperature and global ice volume we present results from an early paleogene configuration of modele r which indicate that spatial gradients of surface ocean 18osw during this period could have been significantly different to those in the modern ocean the differences inferred from modele r are sufficient to change early paleogene sea surface temperature estimates derived from primary carbonate 18o signatures by more than 2 c in large areas of the ocean in the north atlantic indian and southern oceans the differences in 18osw inferred from our simulation with modele r are in direct contrast with those from another 18o tracing model study which used different but equally plausible early paleogene boundary conditions the large differences in 18osw between preindustrial and early paleogene simulations and between models emphasizes the sensitivity of 18osw to climatic and tectonic boundary conditions for this reason absolute estimates of eocene paleocene temperature derived from carbonate 18o alone are likely to have larger uncertainties than are usually assumed

a new paleothermometer for forest paleosols and its implications for cenozoic climate climate is a primary control on the chemical composition of paleosols making them a potentially extensive archive applicable to problems ranging from paleoclimate reconstruction to paleoaltimetry however the development of an effective widely applicable paleosol temperature proxy has remained elusive this is attributable to the fact that various soil orders behave differently due to their respective physical and chemical properties therefore by focusing on an individual order or a subset of the 12 soil orders whose members exhibit similar process behavior a better constrained paleothermometer can be constructed soil chemistry data were compiled for 158 modern soils in order to derive a new paleosol paleothermometry relationship between mean annual temperature and a paleosol weathering index pwi that is based on the relative loss of major cations na mg k ca from soil b horizons the new paleothermometer can be applied to clay rich paleosols that originally formed under forest vegetation including inceptisols alfisols and ultisols and halves the uncertainty relative to previous approaches a case study using cenozoic paleosols from oregon united states shows that paleotemperatures produced with this new proxy compare favorably with paleobotanical temperature estimates global climatic events are also evident in the oregon paleosol record including a 2 8 c drop across the eocene oligocene transition comparable to marine records and a neogene peak temperature during the mid miocene climatic optimum

vegetation and climatic changes of sw china in response to the uplift of tibetan plateau abstract to understand the vegetation succession and climatic changes at the southeastern margin of the tibetan plateau in the neogene we reconstructed the middle miocene vegetation and climate based on palynological data from four localities which are at different latitudes along the ailao mountains in yunnan southwest china the palynological assemblages suggest that the vegetation there was composed of mixed evergreen and deciduous broad leaved forests growing under subtropical conditions based on the palynological data the palaeoclimatic parameters from the four localities are established the new parameters were compared with those of the late miocene of the late pliocene and of today the comparison revealed that the temperatures were obviously lower in the middle miocene than they are today this suggested that the ailao mountains were not high enough to block the asian winter monsoon in the middle miocene the middle miocene vegetation at the southeastern edge of the tibetan plateau was also compared to that of central tibet it would appear that the palaeoclimate at the southeastern edge of the tibetan plateau was warmer and wetter than in central tibet in contrast to the neogene cooling in central europe the climate at the southeastern edge of the tibetan plateau has gradually warmed since the middle miocene this phenomenon was most likely caused by the uplift of the tibetan plateau which has succeeded in blocking the asian winter monsoon since the middle miocene

paleoclimate and paleoecology of the latest eocene florissant flora of central colorado u s a abstract the uppermost eocene florissant formation of central colorado u s a contains a diverse flora and fauna preserved in lacustrine facies and represents a key episode in earth history immediately preceding the eocene oligocene boundary laminated shales contain impressions of non monocot angiosperm leaves that were used to estimate paleoecological and paleoclimatic parameters using leaf physiognomic methods including leaf mass per area ma digital leaf physiognomy dilp leaf margin analysis lma and leaf area analysis laa the majority 58 of the morphotypes analyzed for ma suggested a semi evergreen leaf lifespan whereas another 27 indicated a deciduous habit and 15 an evergreen habit there was no significant relationship between ma and insect damage based on a small subset of florissant s leaves higher ma values 73 of leaves one year lifespan coupled with a tendency toward long and narrow leaf shapes and small leaf areas indicate the existence of sclerophyllous vegetation using the global regression for mean annual temperature mat the dilp estimate of mat was anomalously cold 5 5 4 c however using a northern hemisphere regression the dilp mat estimate of 11 6 3 3 c was more plausible using dilp mean annual precipitation map was estimated at 740 608 334 mm yr 1 which supports dry conditions estimates for mat and map using the univariate lma and laa methods overlapped within uncertainty of the dilp results in addition those taxa classified as growing in wet areas riparian had significantly more teeth than non riparian taxa these paleoclimatic and paleoecological results suggest that outside the riparian forest the florissant flora sampled a seasonally dry temperate sclerophyllous shrubland to woodland perhaps similar to modern chaparral forests in the western interior of the u s a just before the transition into the cooler oligocene