eocene climate record of a high southern latitude continental shelf seymour island antarctica a high resolution record of eocene paleotemperature variation is preserved within the high southern latitude marine shelf succession of the la meseta formation on seymour island off the ne side of the antarctic peninsula 87 sr 86 sr ratios of bivalve shell carbonate indicate that the la meseta formation spans virtually the entire eocene and suggest the presence of an early middle eocene unconformity paleoclimatic and paleoceanographic inferences are based on the stable oxygen and carbon isotope values of two genera of bivalves collected with a high degree of stratigraphic resolution within the formation and with multiple replicate samples from each horizon 18 o data indicate roughly 10 c of cooling from the early eocene climatic optimum 15 c through the end of the eocene minimum 5 c much of which took place in two comparatively short intervals at ca 52 and ca 41 ma many features of the isotope curves generated from this eocene shelf section are apparent in 18 o and 13 c data from the southern and global oceans including warm intervals that likely correspond to the early and middle eocene climatic optima eeco and meco a rapid middle eocene shift to much more positive values is the most signifi cant in the section and refl ects a drop to universally cooler temperatures in the late middle and late eocene that might also be associated with a short lived glacial advance however even using a somewhat depleted value for 18 o of seawater in the antarctic peninsular region average seymour island shelf water paleotemperatures did not reach freezing before the end of the eocene 13 c data similarly refl ect the documented middle eocene surface ocean enrichment followed by more negative values but depletion is much more pronounced on seymour island and persists for the remainder of the eocene suggesting a combination of upwelling metabolic effects and or atypical carbon cycling on the shelf in this region isotope data capture information about changes in the paleoenvironment that also had consequences for the biota as published paleontological records document marked change in the nature of terrestrial and marine biota at this time the fact that middle eocene cooling and biotic turnover in the peninsular region correspond well in time to the proposed initial opening of drake passage suggests that the formation of gateways in addition to changes in pco 2 had signifi cant consequences for the earth s climate system during the paleogene

pedogenic carbonate proxies for amount and seasonality of precipitation in paleosols the depth to carbonate nodular bk horizon in soils d in cm is correlated with mean annual precipitation p in mm so that bk horizons are deep in subhumid regions but shallow in semiarid regions previous quantifications of this relationship are unchanged by this new compilation of 807 soils p 137 24 6 45 d 0 013 d 2 where r 2 0 52 and standard error s e 147 mm in most north american postglacial soils the bk horizon is thin and well defined whereas in monsoonal tropical soils of pakistan and kenya the bk horizon is thick and diffuse data from 675 modern soils define the relationship between the thickness of soil with nodules t in cm and mean annual range of precipitation m in mm difference between monthly means of wettest and driest months m 0 79 t 13 71 where r 2 0 58 and s e 22 mm the relationship between carbonate nodule size s in cm and soil age a in ka is quantified by 9 radiocarbon dated soils from las cruces new mexico a 3 92 s 0 34 where r 2 0 57 and s e 1 8 k y these transfer functions are applied to reconstructing paleoclimatic change from paleocene eocene paleosols of the north horn formation and flagstaff limestone of axhandle canyon utah the terminal paleocene spike of warmth recorded by fossil plants in nearby wyoming was coincident with a brief peak in both mean annual precipitation and mean annual range of precipitation in utah

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

estimating paleoatmospheric pco2 during the early eocene climatic optimum from stomatal frequency of ginkgo okanagan highlands british columbia canada abstract estimates of p co 2 for the early paleogene vary widely from near modern day levels to an order of magnitude greater based on various proxy measures resolving the relationship between climate and p co 2 during this globally warm period is a key task in understanding climate dynamics in a warmer world here we use the stomatal frequency of fossil ginkgo adiantoides from the okanagan highlands of british columbia canada to estimate p co 2 during the early eocene climatic optimum eeco the interval of peak warmth in the cenozoic we also examine a dataset of modern ginkgo biloba leaves to critically assess the accuracy and precision of stomatal frequency as a proxy indicator of p co 2 early eocene fossil g adiantoides has significantly lower stomatal frequency than modern g biloba suggesting p co 2 levels 2 modern pre industrial values this result is in contrast to earlier studies using stomatal frequency of ginkgo that indicated near modern day levels of p co 2 in the early paleogene though not including samples from the eeco we also find that levels of p co 2 as indicated by stomatal frequency are correlated with trends in climate mean annual temperature over time at the falkland fossil locality suggesting that climate and p co 2 were coupled during the eeco hyperthermal

depth to pedogenic carbonate horizon as a paleoprecipitation indicator comment and reply royer 1999 1 has recently used a large data set from the u s natural resources conservation service nrcs to reexamine the relationship between mean annual precipitation and depth to the calcic horizon in soils the extremely poor correlation between these variables in his nrcs data r2 0

high resolution deep sea carbon and oxygen isotope records of eocene thermal maximum 2 and h2 eocene thermal maximum 2 etm2 and h2 were two short lived global warming events that occurred 2 m y after the paleocene eocene thermal maximum petm ca 56 ma we have generated benthic foraminiferal stable carbon and oxygen isotope records of four sites along a depth transect on walvis ridge 3 5 1 5 km paleodepth southeast atlantic ocean and one site on maud rise weddell sea to constrain the pattern and magnitude of their carbon isotope excursions cies and deep sea warming at all sites etm2 is characterized by 3 c warming and a 1 4 cie the h2 event that occurred 100 k y later is associated with 2 c warming and a 0 8 cie the magnitudes of the 13 c and 18 o excursions of both events are signifi cantly smaller than those during the petm but their coherent relation indicates that the 13 c change of the exogenic carbon pool was similarly related to warming during these events despite the much more gradual and transitioned onset of etm2 and h2

do red beds indicate paleoclimatic conditions a permian case study abstract terrestrial red beds have long been interpreted as desert deposits by comparison with modern red deserts more recently red beds have been interpreted as evidence of seasonally dry conditions and a permo triassic pangean monsoon red beds of cala viola sardinia are identified as paleosols and used to reconstruct late permian paleoclimatic conditions reconstruction of paleoenvironmental conditions based on the paleosols of the cala viola indicates warm humid conditions with no evidence of dry conditions as in a desert or of extreme seasonality as in a monsoon instead it is suggested that the red color of the paleosols is a result of former good drainage and that red color in general does not indicate specific paleoclimatic conditions

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

transient drying during the paleocene eocene thermal maximum petm analysis of paleosols in the bighorn basin wyoming abstract the paleocene eocene thermal maximum petm was a transient episode of global warming that occurred at the paleocene eocene boundary the event is marked by a sharp decline in carbon isotope values that is globally recognized from marine and continental sections the negative isotope excursion has been attributed to the release of methane hydrates from oceanic sediments although studies concur that temperatures rose during the petm changes in precipitation are not well understood alluvial paleosols in the bighorn basin that span the petm interval contain a continuous and highly resolved record of climate including information on precipitation they show a significant but transient decrease in precipitation at the onset of the petm but a gradual return to pre petm levels by the end of the interval the paleosols also show additional although less dramatic wet dry cycles within the petm interval that may correspond to precessional cycles that have been identified in the marine record of the petm this study counters interpretations of increased precipitation for wyoming at this time and shows the importance of detailed case studies of continental strata to test climatic generalizations and models that have been developed for petm precipitation patterns

use of carbon isotopes in paleosols as an indicator of the p co2 of the paleoatmosphere measurements of carbon isotopic composition of coexisting paleosol organic matter and carbonate results in improved estimates of the paleo p co2 content of the paleoatmosphere measurements from tertiary paleosols indicate that the levels of co2 in the early eocene middle and late miocene and pliocene were less than 1000 ppmv early cretaceous levels of p co2 were significantly higher of the order of 1500 to 3000 ppmv

water concentration profiles in natural mantle orthopyroxenes a geochronometer for long annealing of xenoliths within magma both mantle derived clinopyroxene and orthopyroxene are generally homogeneous in water concentration while water content in the coexisting olivine is affected by partial or complete loss during the ascent of the hosting magma here we report the first record of water content profiles higher water in the cores than in the rims in natural orthopyroxene grains in peridotite xenoliths hosted by cenozoic alkali basalts in tianchang volcano eastern china the water contents of the coexisting clinopyroxene grains are homogeneous and are twice that measured in the cores of orthopyroxene grains confirming previous chemical equilibrium between the two pyroxenes the olivines ol are nearly dry 0 ppm these observations demonstrate that h diffusion in mantle orthopyroxene opx is faster than in clinopyroxene cpx and the relative mobility of h in each mineral phase could be quantified as dol 10dopx 1000dcpx where d is the chemical diffusion coefficient of hydrogen combining this with experimental diffusion coefficients from the literature we infer that 1 the xenoliths remained in contact with the magma below 900 c for several months and 2 clinopyroxene remains the more reliable recorder of water from depth and orthopyroxene should be used more cautiously but can be considered with olivine for tracing slow transport and cooling of magma

mallee model for mammal communities of the early cenozoic and mesozoic abstract mallee is an endemic australian woodland and shrubland of semi arid summer dry regions between dry woodland and desert shrubland in other parts of the world such as africa and the americas such climatic regions support grassland ecosystems using australian and african climofunctions and models gives very different reconstructions of paleoclimate subhumid versus perhumid and paleovegetation woodland versus rainforest for north american fossil mammal faunas before cenozoic evolution of grassland ecosystems modern mammal faunas of africa and australia have different ecological spectra of taxonomic units body size feeding and locomotion of species of mammals on precipitation gradients gradients in proportions of such categories yield transfer functions for mean annual precipitation from percent species of artiodactyla or macropodidae percent species of moderately large animals 45 180 kg percent species of arboreal mammals and percent species of grazers these transfer functions can be applied to fossil mammal faunas to estimate paleoprecipitation in africa australia and north america modern transfer functions match well paleoprecipitation estimates based on depth to calcic horizons in paleosols at the same localities in kenya and inland australia back through the miocene for fossil mammal faunas of the rocky mountain region of north america african transfer functions fail but australian transfer functions predict paleoprecipitation back to the cretaceous tertiary boundary 66 ma furthermore modern mallee soils investigated in this study closely match cretaceous to eocene paleosols of the rocky mountains extinct mallee like vegetation such as pori woodlands of kenya and cunhaka woodlands newly defined of the rocky mountains better explains the dominance of small nocturnal insectivorous arboreal mammals of paleogene and mesozoic mammal faunas than comparisons with african grassland or rainforest faunas

come a little bit closer a high resolution climate study of the early paleogene laramide foreland the early paleogene greenhouse climate has long captured the attention of researchers however due to limited data and the coarse spatial resolution of general circulation model gcm results it has proven difficult to investigate early paleogene climate at the level of detail characteristic of the actual climate system we present a high resolution regional climate modeling study of the north american laramide foreland our simulation depicts early paleogene climate dynamics in western north america with unprecedented detail increased horizontal resolution improves matches between modeled temperatures and data in some basins however large scale cold biases found in prior gcm simulations persist our study provides insight into the existence of snow and perennial ice in the laramide highlands and northwestern cordillera and describes the summer monsoon along the rocky mountain front in great detail monsoonal precipitation initiates in the southeastern rockies in may penetrates north and west as temperatures warm and peaks at 1 cm day along the southern and central mountain front basins farther to the north and west are drier

determining terrestrial paleotemperatures using the oxygen isotopic composition of pedogenic carbonate abstract quantifying terrestrial paleotemperatures has proven to be a challenging endeavor this paper explores the use of the oxygen isotopic composition of pedogenic calcite for terrestrial paleotemperature reconstructions we generate three paleotemperature equations two of them derived by simultaneous solution of equations that describe the fractionation of oxygen isotopes in the exogenic cycle while the third equation is derived using a linear regression through modern 18occ mat oxygen isotopic composition of pedogenic calcite versus mean annual temperature data we use the paleotemperature equations to evaluate climate change across the k t boundary by analyzing the oxygen isotopic composition of pedogenic carbonates from a series of stacked paleosols in west texas the fabrics in the calcite nodules were evaluated in order to identify soil carbonate components that have the best chance of containing isotopic information that represents ancient pedogenic conditions the average temperature for west texas during the time period studied is 18 0 5 c two temperature excursions are recognized prior to the k t boundary in which terrestrial temperatures increase by about 4 c for relatively short periods of time these short greenhouse events documented in west texas correlate with changes in marine temperatures as well as terrestrial temperatures in north dakota during the same time period latitudinal temperature gradients generated using the west texas and north dakota data indicate that the spatial simultaneous solution yields the most reliable temperature reconstructions of the three equations considered in this study

eocene continental climates and latitudinal temperature gradients global climate during the mesozoic and early cenozoic is thought to have been warmer than at present but there is debate about winter temperatures paleontological data indicate mild temperatures even at high latitudes and in mid latitude continental interiors whereas computer simulations of continental paleoclimates produce winter temperatures closer to modern levels foliar physiognomy and floristic composition of 23 eocene floras from the interior of north america and australia indicate cold month means generally 2 c even where the mean annual temperature mat was

classification of paleosols despite increased interest in paleosols during the past decade no satisfactory classification is in current use presented here is a largely descriptive classification system that utilizes those pedogenic features that have the highest preservation potential in the rock record emphasized in the classification are morphological and mineralogical features that are easily recognizable in the field and through the petrographic microscope the classification is based on evaluation of the relative prominence in a paleosol of six pedogenic features or processes organic matter content horizonation redox conditions in situ mineral alteration illuviation of insoluble minerals compounds and accumulation of soluble minerals the most prominent of these six features processes provides the key to classifying a paleosol into one of nine orders four of the order names are borrowed from soil taxonomy histosol spodosol oxisol vertisol whereas the other five order names are presented here for the first time calcisol gypsisol gleysol argillisol protosol the orders may be preceded by one or more subordinate modifiers that describe other important features of the paleosol the classification is relatively easy to apply to the rock record and should enhance communication and aid in the standardization of terminology

carbon isotope ratio of cenozoic co2 a comparative evaluation of available geochemical proxies 1 the carbon isotope ratio 13c of plant material is commonly used to reconstruct the relative distribution of c3 and c4 plants in ancient ecosystems however such estimates depend on the 13c of atmospheric co2 13cco2 at the time which likely varied throughout earth history for this study we use benthic and planktonic 13c and 18o records to reconstruct a long term record of cenozoic 13cco2 confidence intervals for 13cco2 values are assigned after careful consideration of equilibrium and non equilibrium isotope effects and processes as well as resolution of the data we find that benthic foraminifera better constrain 13cco2 compared to planktonic foraminiferal records which are influenced by photosymbiotes depth of production seasonal variability and preservation furthermore sensitivity analyses designed to quantify the effects of temperature uncertainty and diagenesis on benthic foraminifera 13c and 18o values indicate that these factors act to offset one another our reconstruction suggests that cenozoic 13cco2 averaged 6 1 0 6 1 while only 11 2 million of the last 65 5 million years correspond to the pre industrial value of 6 5 with 90 confidence here 13cco2 also displays significant variations throughout the record at times departing from the pre industrial value by more than 2 thus the observed variability in 13cco2 should be considered in isotopic reconstructions of ancient terrestrial plant ecosystems especially during the late and middle miocene times of presumed c4 grassland expansion

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

influence of retained bitumen in oil prone shales on the chemical and carbon isotopic compositions of natural gases implications from pyrolysis experiments abstract retained bitumen in oil prone source rocks has a significant impact on late gas generation but such influence is still poorly quantified because it is quite difficult to restore the bitumen content retained in a mature source rock in this study a suite of artificially matured samples were prepared from a moderate maturity shale sample to represent shales with different amount of retained bitumen these samples were then pyrolyzed in sealed gold tubes to investigate how the amount of retained bitumen affects the changes in chemical and carbon isotopic compositions of generated gases and the uncertainty of the evaluation of gas maturity and source identification the results indicate that the decrease in yields of hydrocarbon gases is proportional to the reduction of retained bitumen content however a progressive enrichment in heavier carbon isotope 13c of gaseous hydrocarbons occurs while less amount of bitumen is retained in shales this experimental observation partly explains the heterogeneity of methane carbon isotopes for shale gases that have identical thermal maturity levels although the amount of retained bitumen can significantly change the carbon isotopic ratios of individual gas 13c1 13c2 and 13c3 the difference in carbon isotopic composition between gaseous components such as ethane and methane 13c2 13c1 or propane and ethane 13c3 13c2 are not significantly affected and therefore these differential values can be potentially used as maturity indicators for overmature natural gases exhibiting no carbon isotopic reversals geochemical and carbon isotopic diagrams that are widely used for the identification of oil and kerogen cracking gases are also found to be affected by the retained bitumen content these results illustrate that it is necessary to take into account the retained bitumen content of shales when thermal maturity and genetic origin of natural gases derived from oil prone source rocks are being evaluated

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

coupled co2 climate response during the early eocene climatic optimum abstract the early eocene climatic optimum eeco has been characterized as a prolonged warm event indicated by increased atmospheric pco 2 temperatures precipitation and biological turnover a new paleoenvironmental reconstruction using integrated pedological geochemical and isotopic data from the green river basin green river great divide region provides a high resolution record of environmental and climatic change throughout the eeco our reconstruction indicates that this region and likely much of the margin of paleolake gosiute was a stable fluvially controlled floodplain environment with evidence of large scale continuous soil development and features comparable with modern alfisols temperate forest soils regional climate data from multiple proxies indicates that the period was warm temperate and semi arid to sub humid with a peak interval from about 51 5 50 9 ma that exhibits significantly warmer 7 c and wetter 750 mm yr 1 conditions resulting in major changes to the local weathering regime isotopic analyses also indicate a rapid increase to high atmospheric pco 2 values 1700 ppmv and a shift in the 13 c composition of pedogenic carbonates during this peak interval that appear to define and provide a cause for this significant regional response to global climatic change the new data when combined with foraminiferal 13 c records are consistent with co 2 ventilation from a deep marine reservoir source this multi proxy reconstruction suggests that the eeco may have had a superimposed peak of climatic and ecological change on land

a transient rise in tropical sea surface temperature during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been attributed to a rapid rise in greenhouse gas levels if so warming should have occurred at all latitudes although amplified toward the poles existing records reveal an increase in high latitude sea surface temperatures ssts 8 to 10 c and in bottom water temperatures 4 to 5 c to date however the character of the tropical sst response during this event remains unconstrained here we address this deficiency by using paired oxygen isotope and minor element magnesium calcium ratios of planktonic foraminifera from a tropical pacific core to estimate changes in sst using mixed layer foraminifera we found that the combined proxies imply a 4 to 5 c rise in pacific sst during the petm these results would necessitate a rise in atmospheric pco 2 to levels three to four times as high as those estimated for the late paleocene

multi proxy paleosol evidence for middle and late triassic climate trends in eastern utah abstract prior investigations suggest that alluvial lowlands of pangea in the southwestern u s a during the middle to late triassic experienced an arid to semiarid climate with significant seasonality our investigation finds evidence for a global pluvial episode from paleosols in the middle to late triassic section of eastern utah multi proxy paleosol evidence is used to quantify rainfall amounts ambient temperatures and atmospheric co 2 concentrations and infer associated plant formations related to ecosystem persistence rainfall estimates are derived from geochemical molecular weathering ratios temperature and atmospheric co 2 levels from stable oxygen and carbon isotopes of pedogenic carbonate respectively and ecosystem reconstruction by a combination of climate indexes and paleosol characteristics eight pedotypes were identified and include poorly drained aquic entisols fisher well drained non aquic entisols salt valley calcic aridisols castle valley calcic inceptisols moab cambic ute and calcic la sal vertisols dystric inceptisols kokopeli and argillic alfisols slickrock the middle triassic moenkopi formation anisian was dominated by castle valley paleosols with mean annual rainfall between 300 and 400 mm and mean annual temperature between 13 and 23 c mesic to hyperthermic based on these climate indexes and root traces the associated plant formation was most likely desert shrub or dry woodland the lower chinle formation carnian contains a succession of ute and la sal paleosols that changed up section to kokopeli fisher and slickrock paleosols in accordance with geochemical and isotopic signatures from these pedotypes rainfall amounts initially increased to between 700 and 900 mm and then to between 1300 and 1400 mm temperatures estimated from the la sal paleosol are approximately 18 c thermic at this time the lower chinle marks a transition from dry woodland to open forest that appears to correlate with the formation of the petrified forest member in arizona the upper chinle formation carnian norian reveals a return to semiarid to subhumid conditions and the formation of castle valley moab and salt valley paleosols all of which appear to have supported desert shrub or dry woodlands rainfall amounts decreased to between 400 and 600 mm with temperatures eventually increasing to 29 c hyperthermic using the paleosol isotopic barometer atmospheric co 2 estimates generally correlate with other proxy for the triassic the well developed alfisols and noncalcareous inceptisols identified during the carnian of the lower chinle correlate with a previously identified global pluvial episode based on sedimentological and marine isotopic evidence possibly in response to rifting of pangea it should not be assumed that the middle to late triassic in continental alluvial lowlands supported a uniform semiarid to arid climate with strong seasonality

synoptic reconstruction of a major ancient lake system eocene green river formation western united states numerous 40ar 39ar experiments on sanidine and biotite from 22 ash beds and 3 volcaniclastic sand beds from the greater green river piceance creek and uinta basins of wyoming colorado and utah constrain 8 m y of the eocene epoch multiple analyses were conducted per sample using laser fusion and incremental heating techniques to differentiate inheritance 40ar loss and 39ar recoil when considered in conjunction with existing radioisotopic ages and lithostratigraphy biostratigraphy and magnetostratigraphy these new age determinations facilitate temporal correlation of linked eocene lake basins in the laramide rocky mountain region at a significantly increased level of precision to compare our results to the geomagnetic polarity time scale and the regional volcanic record the ages of eocene magnetic anomalies c24 through c20 were recalibrated using seven 40ar 39ar ages overall the ages obtained for this study are consistent with the isochroneity of north american land mammal ages throughout the study area and provide precise radioisotopic constraints on several important biostratigraphic boundaries applying these new ages average sediment accumulation rates in the greater green river basin wyoming were approximately three times faster at the center of the basin versus its ramp like northern margin during deposition of the underfilled wilkins peak member in contrast sediment accumulation occurred faster at the edge of the basin during deposition of the balanced filled to overfilled tipton and laney members sediment accumulation patterns thus reflect basin center focused accumulation rates when the basin was underfilled and supply limited accumulation when the basin was balanced filled to overfilled sediment accumulation in the uinta basin at indian canyon utah was relatively constant at 150 mm k y during deposition of over 5 m y of both evaporative and fluctuating profundal facies which likely reflects the basin margin position of the measured section the most rapid sediment accumulation for the entire system 1 m k y occurred between 49 0 and 47 5 ma when volcaniclastic materials from the absaroka and or challis volcanic fields entered the green river formation lakes from the north our new ages combined with existing paleomagnetic and biostratigraphic control permit the first detailed synoptic comparison of lacustrine depositional environments in all the green river formation basins coupled with previously published paleocurrent observations our detailed correlations show that relatively freshwater lakes commonly drained into more saline downstream lakes the overall character of eocene lake deposits was therefore governed in part by the geomorphic evolution of drainage patterns in the surrounding laramide landscape freshwater overfilled lakes were initially dominant 53 5 52 0 ma possibly related to high erosion rates of remnant cretaceous strata on adjacent uplifts expansion of balanced fill lakes first occurred in all green river formation basins at 52 0 51 3 ma and again between 49 6 and 48 5 ma evaporative underfilled lakes occurred in various basins between 51 3 and 45 1 ma coincident with the end of the early eocene climatic optima and subsequent onset of global cooling defined from marine record however evaporite intervals in the different depocenters were deposited at different times rather than being confined to a single episode of arid climate evaporative terminal sinks were initially located in the greater green river and piceance creek basins 51 3 48 9 ma then gradually migrated southward to the uinta basin 47 1 45 2 ma this history is likely related to progressive southward construction of the absaroka volcanic province which constituted a major topographic and thermal anomaly that contributed to a regional north to south hydrologic gradient the greater green river and piceance creek basins were eventually filled from north to south with absarokaderived detritus at sedimentation rates 1 2 orders of magnitude greater than the underlying lake deposits

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

significance of different modes of rhizolith preservation to interpreting paleoenvironmental and paleohydrologic settings examples from paleogene paleosols bighorn basin wyoming u s a abstract different modes of preservation of root traces rhizoliths provide information on soil moisture regimes in alluvial paleosols in the paleogene fort union and willwood formations of the bighorn basin wyoming u s a this paper links different styles of rhizolith preservation to paleosols whose other pedogenic attributes provide information on ancient soil drainage consequently the paleodrainage significance of different rhizolith preservation patterns is established more confidently rhizoliths consisting of elongate gray mottles rhizohaloes with red rims are common in relatively well drained red paleosols the gray zones are depleted of iron fe whereas the color of the rims indicates hematite accumulation these features are typical of surface water gley processes that caused fe and manganese mn to move from the root channel outward to the soil matrix calcareous rhizocretions either calcareous tubular concretions or micro accumulations of carbonate within gray rhizotubules are also common in moderately well drained red paleosols more poorly drained purple paleosols also have rhizoliths consisting of fe depletion zones however the rhizohaloes are surrounded by yellow brown goethite rims rather than red hematitic rims in many paleosols the red and yellow brown accumulation rims were partly removed by continued depletion producing abundant irregular shaped mottles the nature of the rhizohalo and the color of the fe oxide rim provide information about the intensity of gleying that a paleosol underwent the poorly drained paleosols also show rhizoliths preserved as goethite accumulations contained within gray depletion zones indicating movement of reduced fe from the matrix towards the root channel probably as a result of groundwater gley processes the goethite accumulations are intermingled locally with lignite representing preservation of the root organic material some rhizoliths are preserved as tube shaped concentrations of small 0 1 0 2 mm diameter black spheres whose color indicates a mix of mn and fe oxides these are most common in paleosols with low chroma gray matrix colors indicating very poor drainage the very poorly drained paleosols also show rhizoliths preserved in jarosite which is an oxidation product of pyrite careful observational and geochemical analysis of rhizoliths which are common in continental deposits can help produce a clearer and more thorough interpretation of ancient drainage conditions information about degree of ancient soil wetness or moisture is important for understanding past climatic conditions and for reconstructing terrestrial paleolandscapes

convergent cenozoic co2 history reconstructions of atmospheric carbon dioxide concentrations over the past 65 million years are heading towards consensus it is time for systematic testing of the proxies against measurements and against each other

fe co3 oh in goethite from a mid latitude north american oxisol estimate of atmospheric co2 concentration in the early eocene climatic optimum abstract measured mole fractions x and 13c values of the fe co3 oh component in pedogenic goethite from a mid latitude oxisol of early eocene age 52 ma b p range from 0 0014 to 0 0064 and 20 1 to 15 4 respectively these values of x imply that concentrations of co2 gas in the paleosol were 7400 to 34 000 ppm 13c and 1 x are correlated and define a linear soil co2 diffusive mixing line with a positive slope such positive slopes are characteristic of mixing of two isotopically distinct co2 endmembers atmospheric co2 and co2 from oxidation of soil organic matter from the intercept of the mixing line it is calculated that the 13c value of organic matter in the ancient soil was 28 0 the magnitude of the slope implies an early eocene atmospheric co2 concentration of 2700 ppm a simple model for forest soils suggests that a canopy effect may cause atmospheric co2 concentrations deduced from pedogenic minerals to underestimate the actual concentrations of atmospheric co2 if a significant forest canopy were present at the time of formation of pedogenic goethite in the ione fm the concentration of 2700 ppm calculated for atmospheric co2 could be slightly low but the underestimate is expected to be