atmospheric pco2 since 60 ma from records of seawater ph calcium and primary carbonate mineralogy a 60 m y record of atmospheric p co2 has been refined from knowledge of 1 secular changes in the major ion composition of seawater particularly ca and mg and 2 oscillations in the mineralogy of primary oceanic carbonate sediments both factors have had a significant impact on the chemistry of the ocean carbonate buffer system calculated atmospheric p co2 oscillated between values of 100 300 ppm and to maxima of 1200 2500 ppm from 60 to 40 ma and varied between 100 and 300 ppm from 25 ma to the present the refined p co2 values are significantly lower than previous estimates made from seawater ph data where total dissolved inorganic carbon was assumed constant and more in line with modeling and stomatal index estimations of atmospheric p co2 for the tertiary

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

calcic paleosols their use in subsurface stratigraphy analysis of well log data from cenozoic basin fill of the deer lodge valley southwestern montana provides evidence for identifying paleosols and paleosol stacks in the subsurface the paleosol stacks are continental sequence boundary markers and appear as several relatively thin high velocity high density zones within basin fill zone thickness ranges from 1 to 1 5 m zones are stacked to thicknesses of up to 15 m density varies within the zones by as much as 0 6 g cm3 and differs by as much as 0 9 g cm3 from material immediately above these zones velocity differs by as much as 10 ft ms from the overlying material and causes bright reflections on seismic sections synthetic seismograms are used to tie well log and seismic data basing our interpretation upon well log data and well cuttings analyses we determined the high velocity high density zones to be limestone the pedogenic origin of the limestone is shown by 1 well cutting chips from the high velocity high density zones that exhibit pedogenic features associated with calcic paleosols 2 paleosol horizonation interpreted from well log analysis 3 the absence of minerals normally associated with lacustrine deposits and 4 comparison with surface paleosol exposures

the origin and spread of grass dominated ecosystems in the late tertiary of north america preliminary results concerning the evolution of hypsodonty abstract sediment samples were collected in northwestern nebraska from the following lithologic units 1 the upper oligocene monroe creek formation the lower miocene harrison formation and upper harrison beds of the arikaree group and 2 the lower miocene runningwater formation and the dawes clay member box butte formation of the ogallala group the samples were processed using heavy liquid extraction and analyzed for siliceous plant microfossils phytoliths all samples yielded well preserved and diverse assemblages dominated by grass phytoliths but included phytoliths produced by woody and herbaceous dicotyledons palms and sedges the abundance of woody dicotyledons and palms decreased up section the grass assemblages consisted mainly of festucoid c3 phytolith morphotypes an index assessing the amount of tree cover d p the ratio of dicotyledon phytoliths to grass phytoliths was employed to interpret the data according to this analysis there was open c3 dominated grassland in the study area between 25 and 17 ma at least 7 ma before supposed adaptations to grasslands in ungulates hypsodonty originate

advent of strong south asian monsoon by 20 million years ago abstractthe monsoonal paleoclimate of india has been critical for understanding the tectonic history of himalayan and tibetan uplift over the past 60 my monsoonal circulation in deep time has been inferred from variation in stable isotopes of tooth enamel diatom blooms and dust influx in the indian ocean and the advent of c4 grasses but these proxies are compromised by temperature biotic and source effects our study uses a proxy of carbonate distribution within paleosol profiles to infer appearance of monsoonal circulation of modern strength in the himachal pradesh segment of the himalayan foreland by at least 20 my ago cued to high himalayan deformation and ongoing tibetan plateau uplift and retreat of the paratethys sea paleosol records also demonstrate declining chemical weathering with himalayan and tibetan uplift which was a force for global warming rather than cooling over the past 20 my

constraining the early eocene climatic optimum a terrestrial interhemispheric comparison the early eocene climatic optimum was a period of major climatic and environmental change that was caused by perturbations to the global carbon cycle recent work from terrestrial sections in the northern hemisphere demonstrates that the period was characterized by different responses in the terrestrial and marine realms suggesting that traditional causal mechanisms may not adequately explain the dynamics of the early eocene climatic optimum here we present a new high resolution multiproxy record of terrestrial climatic and environmental conditions during the early eocene climatic optimum from the southern hemisphere and compare this reconstruction to other marine and terrestrial records similar to northern hemisphere terrestrial records there is a transient peak period of atmospheric carbon isotope enrichment as well as increased temperatures and precipitation which indicate that terrestrial environmental responses to the early eocene climatic optimum were broadly consistent in temperate settings worldwide this global consistency in terrestrial records demonstrates differences in peak warming time scales and carbon isotope responses between marine and terrestrial systems which further constrain potential causes for the early eocene climatic optimum to multiple system or nontraditional mechanisms and highlight the importance of paired records for understanding past climate

landforms as extended composite phenotypes biotic influences on geomorphology and vice versa are ubiquitous this paper explores whether landforms may be extended composite phenotypes of biota based on four criteria process form relationships between biota and landforms evolutionary synchrony selective pressure via ecosystem engineering and niche construction and positive feedback benefitting the engineer organism s coral reefs peat bogs biomantles insect mounds grassland soils salt marshes mangrove swamps and some vegetation dependent sand dune types clearly meet these criteria karst landforms meandering rivers and tree uprooting pit mound systems meet the first three criteria but positive feedback to engineer organisms has not been established research in biogeomorphology will surely identify other extended phenotypes implications are that biological evolution will continue to drive landscape metamorphosis the appearance of new landform types and presumably the disappearance of extended phenotypes associated with extinct species independently of extended phenotypes tightly coupled geomorphological ecological interactions such as coevolution and biogeomorphic forms of ecosystem engineering and niche construction are common the toposphere encompassing earth s landforms is partly a biotic construct some elements would be present in an abiotic world but the toposphere would not exist in anything resembling its contemporary state without a biosphere this raises important questions with respect to earth system evolution the bio litho atmo hydro topo and pedospheres coevolve at the global scale major biotic events have driven revolutions in the other spheres but the atmosphere and the global hydrological system seem to have been relatively steady state at the global scale the toposphere and pedosphere have not this suggests that perhaps landforms and soils provide the major mechanisms or degrees of freedom by which earth responds to biological evolution landforms and soils may thus be the voice of the biosphere as it authors planetary change even if clear biotic signatures are lacking copyright 2015 john wiley sons ltd

loess accumulation and soil formation in central kansas united states during the past 400 000 years based on interpolation of thermoluminescence dates and the mean accumulation rate of 0 034 mm yr 1 four cycles of pedogenic caco3 accumulation are found within the loveland loess 415 325 ka 325 250 ka 250 195 ka and 195 95 ka the four caco3 peaks correspond chronologically to marine oxygen isotope stages 11 9 7 and 5 respectively the early wisconsin 95 70 ka was characterized by sand dune activity the reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very slow rate of silt accumulation 0 016 mm yr 1 the gilman canyon pedocomplex enriched in organic matter and dated at 35 20 ka was formed under a strong physical weathering regime and a relatively high rate of silt accumulation 0 15 mm yr 1 indicating a windy relatively moist probably cool environment it developed when the laurentide ice sheet was advancing and dust content in greenland ice core was low the peoria loess was accumulated at a rate of 0 3 mm yr 1 in central kansas under cold dry conditions when the ice sheet fluctuated around its maximum position and the dust content in the greenland ice core was the highest even the warm substage around 13 ka has some corresponding evidence in the central great plains the well developed brady soil dated at 10 5 8 5 ka indicates that the early holocene was the optimal time for soil development since 20 ka the poorly weathered bignell loess might have been deposited during the altithermal period from 8 5 to 6 ka

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

empirical relationships between elevation and the stable isotope composition of precipitation and surface waters considerations for studies of paleoelevation change a compilation of 68 studies from throughout many of the world s mountain belts reveals an empirically consistent and linear relationship between change in elevation and change in the isotopic composition of precipitation along altitudinal transects the isotopic composition of precipitation decreases linearly with increasing elevation in most regions of the world except in the himalayas and at elevations 5000 m there are no significant differences in isotopic lapse rates from most regions of the world 0 28 permil 100 m except at the extreme latitudes where isotopic lapse rates are higher given information on past changes in the isotopic composition of precipitation preserved in pedogenic or authigenic minerals this global isotopic lapse rate can be used to place numerical constraints on the topo graphic development of some ancient mountain belts or plateaus there are many complicating factors that can confound interpretation of paleoel evation change based on stable isotopes and many of these are unique to specific mountain belts or time periods relevant to all stable isotope based paleoelevation change studies is the temperature dependent isotope fractionation between a pedo genic or authigenic mineral and the water from which it forms in cases where isotopic proxy minerals are sampled from localities where temperature will change simulta neously with elevation change the apparent change in the isotopic composition of precipitation may be dampened by several permil this suggests that samples taken from the rainshadow side of an emerging orographic barrier may be more likely to preserve isotopic changes resulting from mountain uplift than samples taken from atop a rising mountain range or plateau

paleoecology of aphelops and teleoceras rhinocerotidae through an interval of changing climate and vegetation in the neogene of the great plains central united states abstract the rhinocerotidae was one of most widespread and abundant mammalian groups in north america during the oligocene and miocene but were extinct by the early pliocene potential drivers of extinction include the expansion of c4 grasslands cooling climate and increased seasonality here we examine potential changes in the relative abundance of two common genera aphelops and teleoceras from the middle miocene to the pliocene of the great plains we also use stable isotopes in tooth enamel to test whether great plains rhinoceroses were able to incorporate c4 vegetation into their diet after the expansion of c4 grasslands relative abundance of rhinoceroses fluctuates during the middle to late miocene but then rapidly declines at the end of the miocene around 6 5 ma coinciding with the expansion of c4 grasslands on the great plains stable carbon isotopes indicate that both aphelops and teleoceras were predominantly c3 feeders for most of their history during c4 expansion some individuals were able to adapt to modest c4 consumption but were not as successful as contemporaneous horses our results suggest that the extinction of rhinoceroses was associated with environmental stress related to diminishing food resources following the expansion of c4 vegetation possibly coupled with a shorter growing season as climate cooled in addition tooth enamel 18o values in rhinoceroses do not support the interpretation that teleoceras a hippo ecomorph had a semi aquatic lifestyle tooth enamel 18o values reflect a strong latitudinal temperature gradient suggesting that rhinoceroses effectively track 18o values in surface waters and are potentially useful for paleoclimatic reconstructions

paleobotanical evidence for high altitudes in nevada during the miocene leaf physiognomy provides estimates of environmental parameters including mean annual enthalpy which is a thermodynamic parameter of the atmosphere that varies with altitude analyses of 12 mid miocene floras from western nevada indicate that this part of the basin and range province stood 3 kilometers above sea level at 15 to 16 million years ago which is 1 to 1 5 kilometers higher than its present altitude much if not all of the collapse to present day altitudes seems to have been achieved by 13 million years ago the crust in much of this area has been extended and thinned throughout the past 40 to 50 million years and the isostatic balance of a thinning crust requires subsidence not uplift as suggested by previous paleobotanical work

equation for compaction of paleosols due to burial existing empirically derived compaction curves for marine sediments fail to estimate the compaction of paleosols flood plain sediments and peats as indicated by deformation of clastic dikes dinosaur footprints and sandstone paleochannels yet compaction estimates are vital to reconstructing paleoclimate and geochemical profiles of paleosols to modeling sediment accumulation rates of nonmarine rocks and to tectonic flexural modeling of molasse facies this paper presents a compaction equation and physically derived constants that make geologically realistic estimates of compaction of paleosols and other nonmarine sediments a protocol for the application of the equation is suggested that would allow the following equation to solve for burial compaction c as a fraction of original thickness given depth of burial d in km as c s i f e d k 1 this equation can be applied to nonmarine sedimentary rocks or paleosols given appropriate empirical data on the physical constants in the equation such as initial solidity s i initial porosity f and the corresponding curve fitting constant k data on physical constants useful for this equation are compiled here for a range of paleosol and nonmarine sediment types

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

pedogenesis and geochemical alteration of the picture gorge subgroup columbia river basalt oregon reddened clay rich horizons between basalt flows have historically been identified as baked zones or as zones of lateral groundwater movement the reddening has been attributed to thermal or chemical alteration of the permeable portion of the basalt flow many of these red horizons are instead paleosols that record significant hiatuses in basalt flow emplacement paleosols were identified in the field on the basis of features such as horizonation ped morphology and root traces terrestrial gastropods fossil plants and peats also occur locally plots of weathering indices such as base loss are consistent with a pedogenic origin for these horizons ca na mg fe 21 and p have been extensively lost from the a and bt horizons of the paleosols consistent with modern weathering patterns k and rb have been added to the upper portions of the profiles and lost in the lower portions of the profiles relative to the parent material with rb added disproportionately historically this pattern of enrichment has been cited as evidence of k metasomatism the apparent metasomatism can be explained using a new model in which there was extensive felsic volcanism contemporaneous with pedogenesis and k and rb were likely added by windborne ash the apparent discordance between k and rb contents of the paleosols can be explained by the presence of land plants because k is an important electrolyte and rb does not serve any major biological role this model could account for apparent k metasomatism in other paleosols following the advent of land plants and may be applicable to older paleosols as well

stable carbon and oxygen isotope shifts in permian seas of west spitsbergen global change or diagenetic artifact we performed petrographic cathodoluminescence electron microprobe and isotopic analyses of brachiopod shells from the permian kapp starostin formation in west spitsbergen to reevaluate the 9 negative shift in 13c and 18o values reported in 1989 by m gruszczynski s halas a hoffman and k malkowski the 13c and 18o values within shells typically decrease with increasing luminescence indicating diagenesis nonluminescent nl shell 13c and 18o values are 4 3 and 6 2 higher respectively than those of associated cements and matrix for the same stratigraphic interval 13c and 18o values of the nl shells are equal to or substantially greater than those reported by gruszczynski et al for the interval where those authors saw a 10 13c shift our mostly nl spiriferella polaris shells only yield a 1 5 shift gruszczynski et al reported a 9 18o shift whereas we observe almost none our results strongly suggest that the 9 isotopic shifts reported in gruszczynski et al are diagenetic artifacts on the other hand their kazanian tatarian 13c maximum of 7 5 is substantiated by our data this late permian 13c maximum represents the highest spiriferid brachiopod 13c values in the phanerozoic and within stratigraphic uncertainty correlates with the whole rock 13c maximum in east greenland and northwestern europe the 13c shift may reflect changes in global storage of organic carbon indicated by coal volume changes in the late permian

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

reconstruction of the late pleistocene grassland of the columbia basin washington usa based on phytolith records in loess abstract silica phytoliths preserved in three loess sections in southeastern washington state revealed a 100 000 year history of the columbia basin grassland changes in the proportion of different morphotypes indicate large shifts in vegetation composition during the last 100 ka a low elevation section 677 m asl near the center of the basin provided a record of alternating xeric festuca poa and mesic festuca koeleria grassland the middle slope section 1095 m asl supported picea abies or pinus ponderosa forest or non analog parkland at different times some trees were present at or near the site even during the last glacial maximum the highest site 1220 m asl supported stipa festuca and poa dominated grassland with some artemisia shrub during most of the late pleistocene but supports a coniferous forest today variations in vegetation can be explained as a response to changes in large scale climatic controls grasslands and shrub steppe were apparently more widespread and forests more restricted than today during the marine isotope stages 2 and 4 probably as a result of cooler and drier conditions the three new records are well correlated with previously published paleo reconstructions based on phytolith cicada burrow and stable isotope data from a nearby kp 1 loess section carp lake pollen record and global ice volume variations

cenozoic deep sea temperatures and global ice volumes from mg ca in benthic foraminiferal calcite a deep sea temperature record for the past 50 million years has been produced from the magnesium calcium ratio mg ca in benthic foraminiferal calcite the record is strikingly similar in form to the corresponding benthic oxygen isotope 18o record and defines an overall cooling of about 12 c in the deep oceans with four main cooling periods used in conjunction with the benthic 18o record the magnesium temperature record indicates that the first major accumulation of antarctic ice occurred rapidly in the earliest oligocene 34 million years ago and was not accompanied by a decrease in deep sea temperatures

vegetation response during the lead up to the middle miocene warming event in the northern rocky mountains usa abstract the mid miocene climatic optimum mmco initial warming beginning ca 18 ma and with peak warming ca 17 14 75 ma constitutes the earth s most recent greenhouse episode characterized by a transient shift to higher global atmospheric co 2 levels and warmer possibly wetter climatic conditions combined with the spread of grass dominated habitats it has been suggested that the mmco lead to significant turnover and modernization of fauna and flora however records documenting local vegetation change during the mmco are rare hence this hypothesis remains largely untested herein we combine phytolith assemblages and 13 c records from paleosol organic matter from the railroad canyon section rcs eastern idaho to provide the first direct detailed and continuous long term record of vegetation composition and structure in a single basin during the lead up to the mmco 22 9 15 2 ma late arikareean early barstovian phytolith assemblage analysis indicates that grasses primarily c 3 pooids dominated early middle miocene vegetation potential c 4 pacmad grasses were present by ca 21 6 20 7 ma late arikareean and vary in abundance 0 4 17 2 of diagnostic phytoliths through the section although relatively rare overall pacmad grasses decrease significantly through time in parallel with declining diatom abundances and an increase in pooid grasses in contrast paleosol 13 c org indicates 0 29 1 c 4 vegetation but no consistent temporal change where both phytolith and isotope based estimates are made from the same paleosol they are within error most 82 of the time thus the apparent discrepancy in temporal trends could either be due to differences in the resolution of the two records or could be explained if many pacmads were not c 4 grasses but instead water loving c 3 species overall these data suggest that open habitat mosaic vegetation with grass dominated grasslands and open woodlands occurred in the north rocky mountains usa by at least the early miocene more comparable to the timing for the spread of grass dominated habitats in the great plains than previously thought additionally phytolith data suggest that overall vegetation structure remained relatively stable throughout the rcs inconsistent with published paleosol morphology data this points to regionally unique floral patterns decoupled from global climate change leading into the mmco

eocene vegetation and ecosystem fluctuations inferred from a high resolution phytolith record a thorough understanding of the ecosystem factors that can act as drivers of vegetation change an important factor for projecting impacts of future climate change requires adequately distinguishing between plant community changes that occur on the local scale or over ecological time scales and long term trends phytolith assemblages have the potential to provide this information but little work has been done so far to test their ability to do so in deep time we examined vegetation patterns inferred from phytoliths plant silica microfossils from a single section of the renova formation timberhills region montana dated to 39 2 3 ma late middle eocene the section is composed of fl uvial sediments overprinted by paleosols including alfi sols entisols inceptisols and composite paleosols phytolith assemblages from 27 paleosol samples were used to reconstruct a high resolution vegetation history for the area and were compared with paleosol data phytoliths are predominantly from forest plants and include tropical elements such as palms arecaceae and gingers zingiberales suggesting a paratropical forest the high resolution sampling records heterogeneous vegetation including shifts among closed forest moderately open forest forest gaps edges and woodland and grass dominated habitats grasses are interpreted as early open habitat plants tolerant of drier conditions but they appear to be replaced by forest vegetation with time resulting in poor correspondence between paleosol type and phytolith assemblage at some stratigraphic levels where paleosol morphology indicates a forest ecosystem and the phytolith assemblages indicate a changing grass forest mixture as a function of depth within the profi les this is the fi rst study that has used phytoliths to construct a high resolution record of vegetation from deep time and we demonstrate that dense sampling and multiproxy approaches to paleo environmental reconstruction are necessary to capture vegetation heterogeneity in time and across microhabitats

middle cenozoic uplift and concomitant drying in the central rocky mountains and adjacent great plains when and how the central rocky mountains rockies of western north america gained modern topography remain controversial questions we reconstruct the middle and late cenozoic topography along a transect that extends from the great plains of western nebraska across the central rockies in wyoming based on reconstructed surface water d values from volcanic glass d values our data show gradual increases of surface water d values in both the central rockies and adjacent great plains during middle and late cenozoic time and the establishment of a similar to present surface water d gradient between the central rockies and western great plains before earliest oligocene time these observations suggest that the region underwent differential uplift to form relief similar to that of today before earliest oligocene time this uplift has caused regional drying and the gradual increase of surface water d values over the past 35 m y when placed in the context of other paleoaltimetry studies our work suggests that along our transect the central rockies and adjacent great plains underwent uplift during the late eocene and have not undergone any large magnitude 500 m uplift since that time

tertiary history of c4 biomass in the great plains usa we use the carbon isotope composition of paleosols to reconstruct the history of c4 biomass on the great plains from ca 23 to 1 ma the proportion of c4 biomass was uniform and moderate 12 34 throughout the miocene increased between 6 4 and 4 0 ma and reached modern levels by 2 5 ma ecological changes in great plains ungulates preceded the increase in c4 biomass the contrasts in the paleosol and ungulate records may indicate initial development of c3 grasslands after the middle miocene or a greater role for ecological interactions within communities in structuring ungulate faunas contrasts in paleosol records from different continents point to regional rather than global controls on the evolution of c4 grasslands

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

refining a pedogenic carbonate co2 paleobarometer to quantify a middle miocene greenhouse spike abstract estimates of respired soil co2 concentration in paleosols are needed to calculate past atmospheric co2 levels from the difference between organic and carbonate carbon isotopic values in paleosols a new compilation of co2 concentrations late in the growing season in modern calcareous soils can be used to estimate respired soil co2 by subtracting atmospheric co2 concentrations furthermore respired co2 shows a significant relationship with depth to calcic horizon and this relationship can be used to estimate respired co2 concentrations in paleosols these values as well as estimates of 13c of atmospheric co2 from 13c of soil organic matter and of paleotemperature from bw horizon chemical composition refine the cerling co2 paleobarometer these refinements are applied to quantify the middle miocene greenhouse which has been controversial because it was not detected by marine alkenone and boron paleobarometers new estimates of middle miocene atmospheric co2 from paleosols in railroad canyon idaho reveal levels at 16 ma of 852 86 ppmv this is similar to predicted values by 2100 and 3 times pre industrial values pil 280 ppmv

modeling the ries steinheim impact event and the formation of the moldavite strewn field using detailed geological petrographic geochemical and geographical constraints we have performed numerical modeling studies that relate the steinheim crater apparent diameter da 3 8 km the ries crater da 24 km in southern germany and the moldavite tektite strewn field in bohemia and moravia czech republic lusatia east germany and lower austria the moldavite strewn field extends from 200 to 450 km from the center of the ries to the east northeast forming a fan with an angle of 57 an oblique impact of a binary asteroid from a west southwest direction appears to explain the locations of the craters and the formation and distribution of the moldavites the impactor must have been a binary asteroid with two widely separated components some 1 5 and 0 15 km in diameter respectively we carried out a series of three dimensional hydrocode simulations of a ries type impact the results confirm previous results suggesting that impacts around 30 50 from the horizontal are the most favorable angles for near surface melting and consequently for the formation of tektites finally modeling of the motion of impact produced tektite particles through the atmosphere produces in the downrange direction a narrow angle distribution of the moldavites tektites in a fan like field with an angle of 75 an additional result of modeling the motion of melt inside and outside the crater is the preferred flow of melt from the main melt zone of the crystalline basement downrange towards the east northeast rim this explains perfectly the occurrence of coherent impact melt bodies some tens of meters in size in a restricted zone of the downrange rim of the ries crater the origin of these melt bodies which represent chemically a mixture of crystalline basement rocks similar to the main melt mass contained as melt particles 0 5 m in size in the suevite do not occur at any other portion of the ries crater rim and remained enigmatic until now although the calculated distribution of moldavites still deviates to some degree from the known distribution our results represent an important step toward a better understanding of the origin and distribution of the high velocity surface melts and the low velocity deep seated melt resulting from an oblique impact on a stratified target

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

coupling of marine and continental oxygen isotope records during the eocene oligocene transition while marine records of the eocene oligocene transition indicate a generally coherent response to global cooling and the growth of continental ice on antarctica continental records indicate substantial spatial variability marine eocene oligocene transition records are marked by an 1 1 foraminiferal 18o shift but continental records rarely record the same geochemical signature making both correlation and linking of causal mechanisms between marine and continental records challenging here a new high resolution continental 18o record derived from the freshwater gill breathing gastropod viviparus lentus is presented from the hampshire basin uk the solent group records marine incursions and has an established magnetostratigraphy making it possible to correlate the succession directly with marine records the v lentus 18o record indicates a penecontemporaneous higher magnitude shift 1 4 than marine records which reflects both cooling and a source moisture compositional shift consistent with the growth of antarctic ice when combined with clumped isotope measurements from the same succession about half of the isotopic shift can be attributed to cooling and about half to source moisture change proportions similar to marine foraminiferal records thus the new record indicates strong hydrological cycle connections between marine and marginal continental environments during the eocene oligocene transition not observed in continental interior records

sequence stratigraphy of cenozoic continental rocks southwestern montana because the presently used bozeman group lithostratigraphy is difficult to apply to cenozoic basin fill rocks in the jefferson beaverhead melrose and divide valleys southwestern montana we advocate the use of sequence stratigraphy surface sequence boundaries are in many cases marked by calcic paleosol zones these zones can be projected into the subsurface and tied to seismic reflection data density velocity contrasts between calcic paleosol zones and overlying nonpedogenic rocks generate bright reflectors that define sequence boundaries sequence boundary delineation is further enhanced by reflection termination patterns similar to those found in marine strata sequence age calibration is based upon vertebrate fossil and radiometric age data five sequences separated by basin wide unconformities are recognized most sequence bounding unconformities are marked by paleosols an occurrence not previously reported for cenozoic strata of southwestern montana the sequences and their age ranges are 1 bridgerian uintan approximately 50 to 44 ma calc alkaline volcanic flows and interstratified sedimentary rocks 2 duchesnian to whitneyan approximately 42 to 30 ma terrestrial sedimentary and volcanic rocks 3 arikareean approximately 27 to 21 ma terrestrial sedimentary and volcanic rocks 4 barstovian to blancan approximately 16 to 4 ma terrestrial sedimentary and volcanic rocks and 5 early quaternary approximately 1 8 ma to holocene terrestrial sedimentary and volcanic rocks

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

cenozoic expansion of grasslands and climatic cooling abstract mountains ocean currents forests and swamps have played an important role in regulating global climate for hundreds of millions of years but the truly novel event of the cenozoic was the evolution and expansion of grasslands with their uniquely coevolved grasses and grazers neogene expansion of the climatic and geographic range of grasslands at the expense of woodlands is now revealed by recent studies of paleosols fossils and their stable isotopic compositions grasslands and their soils can be considered sinks for atmospheric co2 ch4 and water vapor and their cenozoic evolution a contribution to long term global climatic cooling grassland soils are richer in organic matter than are woodland and desert soils of comparable climates and when eroded their crumb clods form sediment unusually rich in organic matter grasslands also promote export of bicarbonate and nutrient cations to lakes and to the oceans where they stimulate productivity and c burial this increased productivity and

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

new constraints on using paleosols to reconstruct atmospheric pco2 ecosystem and climatic changes due to anthro po genic emissions of co 2 are of increasing importance to society one way to predict these changes in the future is to study warming events in the geologic past the main control of earth s temperature over geologic time is the concentration of atmospheric co 2 however the precise relationship between co 2 and temperature is not fully understood therefore it is essential to be able to quantify atmospheric co 2 concentrations in the geologic past especially at times of rapid climate change analogous to current atmospheric changes one widely applied proxy relates the carbon isotopic composition of pedogenic carbonates to atmospheric pco 2 but one of the key variables soil respired co 2 s z is not well constrained this study presents a new proxy where soil respired co 2 is related to mean annual precipitation map by the following equation s z 5 67 map 269 9 r 2 0 59 se 681 ppm this proxy validated for modern atmospheric pco 2 levels constrains the primary source of uncertainty in the soil carbonate paleobarometer we apply this proxy to make atmospheric pco 2 reconstructions for examples from the cenozoic mesozoic and paleozoic and calculate co 2 estimates that are in better agreement with estimates from other independent proxies and model results than previous pedogenic carbonate reconstructions the implications of the uncertainties attributed to pedogenic carbonate paleobarometry as well as guidelines for using this method are discussed by making individual measurements rather than assumptions for each isotopic value and combining those analyses with an s z estimate for each paleosol considered using our new proxy described herein we can obtain increased precision for atmospheric pco 2 reconstructions

magnetostratigraphic chronology of cretaceous to eocene thrust belt evolution central utah usa the axhandle basin in central utah is a piggyback basin that formed above the gunnison thrust system the basin contains 1 km of upper cretaceous to eocene strata of the north horn and lower flagstaff limestone formations a significantly more exact chronology based on magnetic polarity stratigraphy has been developed for the basin filling strata the new data provide a detailed temporal framework for the interpretation of the depositional and tectonic evolution of the basin during chrons 33 21 75 49 ma tectonic subsidence curves and stratigraphie relations along the eastern basin margin define two episodes of motion on the gunnison thrust system the majority of tectonic shortening on the system occurred between 83 75 ma and caused widespread non deposition within the axhandle basin a second episode of motion in detail comprising of four separate periods of backthrusting occurred between 70 60 ma the canyon range pavant and nebo thrust sheets were emplaced 30 50 km to the west of the axhandl

the role of fractional crystallization magma recharge and magma mixing in the differentiation of the small hasandag volcano central anatolia turkey abstract during the last 7 ma eruptions of the small hasandag composite volcano in central anatolia turkey have produced calc alkaline lavas ranging in composition from basalt to rhyolite published research on this volcano suggests that crystal fractionation and magma mixing are the two important processes controlling the differentiation of the small hasandag magmas the shortcomings of previous studies are that neither the intensive variables p t fo2 nor the constraints under which the presumed parental magmas evolved have been quantitatively evaluated in this study we have used the melts algorithm of ghiorso and sack 1995 to determine the initial system parameters in terms of temperature t pressure p oxygen fugacity fo2 and water content wt h2o and then evaluated the consequences of magma differentiation under closed system fractional crystallization magma recharge and magma mixing conditions separately in order to determine the initial system parameters we carried out approximately 100 isobaric fractional crystallization simulations of the parental basaltic andesite magma mg 68 in the pressure range of 1 bar to 10 000 bars an fo2 range of qfm 1 to qfm 3 and at water contents from 0 to 4 wt the best agreement between the computed melt compositions and the natural rocks was achieved at p 1000 bars fo2 qfm 1 and 2 wt water computations with parental basaltic andesite at these initial system conditions and under isobaric fractional crystallization generated melt compositions from basaltic andesite to dacite that are very similar to observed lava compositions compositions more evolved than dacites however cannot be produced by closed system fractional crystallization alone this is because rhyolites generated by closed system fractional crystallization have total alkali na2o k2o values lower than those of the small hasandag rhyolites furthermore natural rock compositions in the silica range of 62 65 wt show discrete cycles of sudden increase and decrease in the mgo content in the range of 0 5 1 wt suggesting magma replenishment this study shows that fractional crystallization and magma recharge in the composition range of basaltic andesite to dacite followed by isobaric isenthalpic mixing of dacite with the most differentiated rhyolite mg 46 generate melt compositions that most closely resemble the entire compositional range of the small hasandag lavas including the rhyolites the agreement between the liquid line of descent defined by the natural lavas and melts calculations and the agreement between the observed mineralogy of the rocks and the calculated order of crystallization support this conclusion

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

the influence of explosive volcanism on fluvial sedimentation the deschutes formation neogene in central oregon abstract the upper miocene to lower pliocene deschutes formation of central oregon is a sequence of interstratified volcanic and sedimentary rocks as much as 700 m thick largely derived from the adjacent cascade range the formation is correlative with the early high cascade eruptive episode that included voluminous pyroclastic eruptions and culminated in the development of an intra arc graben in the central oregon high cascades facies associations and paleocurrent data define three depositional settings 1 the eastward sloping arc adjacent alluvial plain was the depositional site by sheetfloods debris flows and hyperconcentrated flood flows their deposits from 10 to 70 m thick sequences separated by erosion surfaces with up to 60 m of relief widespread superimposed paleosols overlie these facies and constitute the upper 10 to 50 m of the section sedimentation was episodic with pulses of rapid aggradation corresponding to periods of explosive volcanism and abundant sediment supply separated by periods of nondeposition when streams incised to reestablish grade as sediment loads diminished 2 a gravel bedload river flowed northward through the basin at the foot of the alluvial plain and is represented by channel fill conglomerates and overbank sandstones and siltstones 3 a thin sequence derived from older tertiary highlands was deposited on the east side of the basin and was little affected by cascade volcanism extensive development of thick superimposed paleosols reflects the inactive nature of the eastern basin margin as a sediment source deschutes formation deposition records the response of a fluvial system to large volcanism induced sediment loads popular facies models do not adequately allow for the influence of volcanism on fluvial systems because sediment is mobilized episodically and on a scale unparalleled in nonvolcanic settings

reconstructing the paleotopography of mountain belts from the isotopic composition of authigenic minerals the paleorelief of mountain belts can be estimated from the 18 o value of authigenic minerals development of relief during mountain building often creates lee side rain shadows in which precipitation is depleted in 18 o and d the magnitude of this rain shadow effect is strongly correlated to relief a compilation of 18 o data from surface waters throughout the globe shows a linear relationship between net elevation change and 18 o r 2 0 79 through the use of this relationship we investigated the timing and magnitude of elevation change in the southern alps of new zealand and the sierra nevada of california the 18 o values of kaolinites from new zealand show an 6 decrease in the early pliocene that corresponds to an 2 km elevation change in the southern alps the 18 o of smectites from the sierra nevada show little change since 16 ma suggesting that these mountains have been a long standing topographic feature

terrestrial evidence for a two stage mid paleocene biotic event abstract marine records of the paleocene indicate a series of hyperthermal events characterized by significant climatic and carbon cycle variability but there are few comparable continental records the mid paleocene biotic event mpbe is a recently described interval defined by a rapid negative carbon isotope excursion and major short term changes in marine ecosystems but it is as yet unclear whether the event was globally important here we present the first terrestrial paleoenvironmental record of the mpbe based on paleosols that document rapid and short lived increases in temperature and precipitation and resultant shifts in plant assemblages concomitant with substantial carbon isotope excursions the new record indicates that carbon cycle changes during the early late paleocene may have resulted in a two stage transient hyperthermal event that caused a significant perturbation to both the regional climate and terrestrial ecology of south america in addition to the major biotic event mpbe previously recognized in marine records overall this suggests that the mpbe may have been a global climate event with far reaching environmental impacts in both the marine and terrestrial realms

regional paleoprecipitation records from the late eocene and oligocene of north america abstract the marine 18o record indicates precipitous cooling or significant expansion of antarctic ice volume across the eocene oligocene epoch boundary at 33 7 ma this climatic step is also found in estimates of decreased paleoprecipitation from paleosols in oregon montana and nebraska but is only a part of a long term decline across the eocene oligocene transition rather than a sudden shift this suggests that climate was driven by a gradual process rather than a single perturbation paleoprecipitation levels stabilized during the oligocene coincident with a stabilization in 18o values possibly indicating a new climatic steady state

a high resolution micromorphological record of the late quaternary paleosols from ganga yamuna interfluve stratigraphic and paleoclimatic implications abstract this study reports the micromorphological record of a continuous set of samples from paleosol bearing intervals of two subsurface cores of 50 m depth representing typical pedosedimentary sequences of the ganga yamuna interfluve in the western ganga plains micromorphology microstructures rhizocretes fe mn features pedogenic carbonate illuvial clay coatings and relict pedofeatures was used to characterize pedogenic processes in the 13 paleosols in the iitk core and the 10 paleosols in the bhognipur core formation of these paleosols took place through incipient to moderate weathering on relatively stable surfaces of the ganga yamuna interfluve over the last 100 ka these paleosols range in character from simple ones having weakly developed pedofeatures to mature paleosols with strongly developed pedofeatures and are similar to modern entisols inceptisols alfisols and vertisols of the ganga plains pedosedimentary evolution in the two interfluve successions differs in terms of stratigraphic stacking of paleosols types of paleosols and heterogeneous nature of sediments in the northern part the iitk interfluve core is marked by a thick mature paleosol with a strongly developed argillic bt horizon at 41 45 m depth and weakly developed paleosols in the remaining part of the core the mature paleosol represents a major discontinuity when prolonged pedogenic activity took place on stable surfaces with little or no deposition on the other hand thin simple thick cumulic paleosols with weakly developed pedogenic features even with some preservation of sedimentary laminations indicate short stratigraphic breaks in rapidly aggrading sediments in the southern part the bhognipur core is marked by the heterogeneous nature of sediments with a predominance of cratonic sediments in the lower part and the himalayan sediments in the upper parts in contrast the iitk core shows a himalayan source throughout the entire interfluve succession in the bhognipur region is marked by rapid sedimentation and short pedogenic intervals of weakly developed paleosols excepting one mature paleosol with well developed argillic bt and vertic bss horizons at 10 14 m depth this mature paleosol possibly formed synchronously with a mature paleosol from the northern part of this interfluve the mature paleosol in both the cores represents a major stratigraphic break of 8000 10 000 years when prolonged pedogenesis occurred over large areas of the ganga yamuna interfluve following regional degradation and local gullying in response to climate change from sub humid to semi arid conditions during the mis 5 4 transition

chlorophyll dispersal by eddy eddy interactions in the gulf of mexico 1 a lagrangian analysis of the transport and dispersal of plumes observed in satellite derived ocean color images was conducted using a data assimilating model of the gulf of mexico the interaction between pervasive cyclonic and anticyclonic eddies in the gulf generated advective paths that connect remote shelf regions these paths aligned remarkably well with the plume events recorded with the chlorophyll a ocean color product from seawifs two such events were studied in one event material was transported in a thin strip between the northern wall of the loop current and an adjacent cyclone connecting the eastern campheche shelf off the yucatan peninsula and south florida shelves the other event began off the louisiana shelf break as a small plume traced by chlorophyll and then developed into a long and thin feature which meandered to the shelf break off the northern yucatan peninsula moving between a large anticyclone and several adjacent cyclones these results indicate that inter eddy advection plays a crucial role in developing the ocean color patterns observed in the satellite ocean color data

eocene oligocene extinction and paleoclimatic change near eugene oregon thick ash fl ow tuffs provide marker beds through fossiliferous eocene and oligocene marine and non marine sedimentary rocks near eugene oregon new mapping radiometric dating and paleomagnetic stratigraphy of these tuffs and rocks now allow dating of local fossil fl oras the comstock goshen rujada and willamette fl oras have been widely used as evidence for eocene oligocene climatic cooling and drying eocene leaves from comstock and hobart butte included such thermophilic taxa as liquidambar the early oligocene goshen fl ora lacked liquidambar but retained many thermophilic species with large leaves that have entire margins and acuminate apices drip tips in contrast fossil leaves from later oligocene rujada and willamette fl oras are small and serrate and most lack drip tips marine faunas also indicate climatic cooling and local disappearance of thermophilic molluscs such as anadara ficus and conus our dating and compilation of plant and molluscan fossil occurrences indicate a steady rise in species diversity from 46 ma to maximal diversity of thermophilic taxa at 35 34 ma then extinctions of 60 of plant species after 33 4 ma and 32 of marine invertebrates after 33 2 ma both signifi cantly postdating the eocene oligocene boundary at 33 7 ma plant diversity rebounds during the early oligocene but marine invertebrates continue to decline into the oligocene in part due to the retreat of fully marine environments from the eugene area neither these data nor evidence from coeval fossil plants and soils in central oregon support the notion of a terminal eocene event nor any other single abrupt paleoclimatic shift or extinction the eocene oligocene biotic and climatic transition was drawn out over some 6 m y abrupt forcings such as meteorite impacts or volcanic eruptions are less likely explanations for cooling and diversity decline than long term processes such as mountain building changing ocean currents or reorganization of the carbon cycle by coevolution of grasses and grazers

petrography and stable isotope geochemistry of oligocene miocene continental carbonates in south texas implications for paleoclimate and paleoenvironment near sea level abstract cenozoic sedimentary rocks in the southern texas gulf coastal plains contain abundant continental carbonates that are useful for reconstructing terrestrial paleoclimate and paleoenvironment in a region near sea level our field observations and thin section characterizations of the oligocene and miocene continental carbonates in south texas identified three types of pedogenic carbonates including rhizoliths carbonate nodules and platy horizons and two types of groundwater carbonates including carbonate cemented beds and carbonate concretions with distinctive macromorphologic and micromorphologic features based on preservations of authigenic microfabrics and variations of carbon and oxygen isotopic compositions we suggest these carbonates experienced minimal diagenesis and their stable isotopic compositions reflect paleoclimate and paleoenvironment in south texas our oligocene and miocene carbonate clumped isotope temperatures t 47 are 23 28 c slightly less than or comparable to the range of modern mean annual and mean warm season air temperature 21 27 c in the study area these t 47 values do not show any dependency on carbonate type or trends through time suggesting that groundwater carbonates were formed at shallow depths these data could indicate that air temperature in south texas was relatively stable since the early oligocene the reconstructed paleo surface water 18o values are similar to modern surface water which could indicate that meteoric water 18o values also remained stable since the early oligocene mean pedogenic carbonate 13c values increased 4 6 during the late miocene most likely reflecting an expansion of c4 grassland in south texas this study provides the first mid and late cenozoic continental records of paleoclimate and paleoecology in a low latitude near sea level region

climatic signals from loess soil sequences in the central great plains usa abstract late quaternary eolian deposits and buried soils in the central great plains are interpreted to reflect the fluctuation of climatic conditions under which they formed the loveland loess was deposited approximately between 500 and 100 ka within the loess are four zones of pedogenic carbonate accumulation after 416 35 ka before 260 25 ka around 193 22 ka and before 92 7 0 ka the pedogenic carbonate zones were probably formed under warm and dry conditions the moderately weathered barton sand at the barton section and the equivalent sandy silt ii at other sections deposited between 92 7 0 and 69 6 4 ka suggest windy probably warm and fluctuating moisture consitions a reddish pedocomplex was formed from 70 to 35 ka under relatively warm and moist climatic conditions with a very low rate of loess deposition overlying the reddish pedocomplex is the sandy silt i probably a stratigraphic equivalent to the roxana silt dated at 40 30 ka in the central lowlands the gilman canyon formation 35 20 ka a thick cumulic loessial and organic matter rich pedocomplex developed under relatively moist and probably cool conditions the peoria loess was deposited at a very rapid rate under dry and cold conditions the brady soil 10 5 8 5 ka was formed under relatively warm and moist conditions the poorly weathered bignell loess was deposited during the warm and dry altithermal period 9 5 ka

faunal burrows as indicators of paleo vegetation in eastern washington usa abstract the palouse loess deposits in the pacific northwestern united states contain buried paleosols with distinctive biological fabrics the washtucna soil formed 40 000 15 000 yr ago during the last full glacial contains up to 90 by volume distinctive cylindrical pedotubules that are 1 2 cm in diameter formed by burrowing fauna the overlying post glacial loess and modern surface soils that support perennial grasslands lack these cylindrical burrows we investigated the paleoecological significance of the burrows observations of several types of burrowing fauna under native vegetation indicated that nymphs of cicadas homoptera cicadidae are responsible for cylindrical back filled burrows that match those in the washtucna soil we measured the abundance of active cicada burrows in soils in four native vegetation zones soil sites establishing that cicada burrows comprise 19 of the rooting zone volume in sagebrush steppe but just 1 3 of the rooting zone volume in bunchgrass steppe meadow steppe and coniferous forest this suggests strongly that abundant cicada burrows in paleosols are a proxy for the geographic extent of plant communities that contained sagebrush to assay the activity of cicada nymphs through time we measured burrowed volume by depth from the soil surface down through the washtucna soil i e from the present to ca 40 000 yr bp at five stratigraphic research sites paleosol sites cicada burrowed volume is generally less than 5 in the rooting zone of the surface soils and throughout holocene loess but is up to 94 in the rooting zone of the washtucna soil at paleosol sites that currently support bunchgrass steppe outside the present day sagebrush steppe zone cicada host preferences in vegetation zones today suggest that sagebrush was the dominant shrub as the washtucna soil formed from this reconstruction combined with information from studies of pollen and plant opal we infer that periglacial steppe plant communities dominated by sagebrush spread from 40 000 to 15 000 yr bp into areas of the columbia plateau that support bunchgrass steppe meadow steppe and even some coniferous forest today trace fossils of soil fauna in paleosols are indicators of fluctuations in biological activity in response to climatic changes of the quaternary period in palouse loess deposits

dissolution effects on foraminiferal mg ca records of sea surface temperature in the western equatorial pacific 1 mg sea surface temperature sst records from different planktonic foraminifera g sacculifer and g ruber size fractions and core depths 1600 and 2600 m suggest similar amplitudes of cyclic change over the last 425 kyr however there are significant differences in the detail recorded by different size fractions and between cores in close geographic proximity these differences may be induced by dissolution but artifacts resulting from divergent cleaning protocols and a dependency of the magnitude of these on preservation status cannot be ruled out these and issues such as reproducibility require greater scrutiny for the true significance and credibility of down core mg sst variability to be established

onset of asian desertification by 22 myr ago inferred from loess deposits in china the initial desertification in the asian interior is thought to be one of the most prominent climate changes in the northern hemisphere during the cenozoic era1 2 3 4 but the dating of this transition is uncertain partly because desert sediments are usually scattered discontinuous and difficult to date here we report nearly continuous aeolian deposits covering the interval from 22 to 6 2 million years ago on the basis of palaeomagnetic measurements and fossil evidence a total of 231 visually definable aeolian layers occur as brownish loesses interbedded with reddish soils this new evidence indicates that large source areas of aeolian dust and energetic winter monsoon winds to transport the material must have existed in the interior of asia by the early miocene epoch at least 14 million years earlier than previously thought3 5 regional tectonic changes and ongoing global cooling are probable causes of these changes in aridity and circulation in asia

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

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