biological remains geochemistry and stable isotopes for the reconstruction of environmental and hydrological changes in the holocene lakes from north sahara abstract a detailed reconstruction of the holocene palaeoenvironments and palaeohydrology is presented for wwamp and lacustrine calcareous sediments which lie in closed depressions along the northern margin of the great western erg algeria it is based on a multidisciplinary approach using numerous techniques the chronological framework is established on the basis of 23 14 c dates on inorganic calcite and mollusc shells ranging from ca 9300 to 3000 yr b p and on an isolated 14 c age of ca 10 900 yr b p the significance of various environmental markers is discussed biological remains are abundant and diversified about 150 taxa including diatoms chrysophytes charophytes ostracods molluscs and foraminifera they provide information on the water chemistry total salinity ionic ratio ph and partial pressure of carbon dioxide and on the habitats water depth development of aquatic plants ephemerality etc emphasis is given to the total salinity individual organisms and palaeobiological assemblages are ordered as a function of their salt requirements and tolerances calibration based on modern diatom samples allows a tentative estimate of the palaeosalinities which range from fresh to marine like and even hypersaline waters attention is drawn to the possible colonization of marine organisms in continental basins without any connection with the sea stable isotope analyses have been carried out on both inorganic and biogenic mollusc and ostracod shells charophyte gyronites carbonates the 18 o contents demonstrate wide changes in the hydrological balance fluctuations in 13 c contents inform on water mixing residence time and on the importance of biological effects on total dissolved inorganic carbon geochemical analyses were performed on inorganic calcite and on ostracod shells high contents in fe and mn indicate reducing environments during stages of high salinity sr ca and mg ca are used as salinity indicators zn mg ratios suggest that the major water supply was the aquifer of the great western erg today down to about 50 m rather than surface waters from the atlas mountains salinities resulted from the balance between inputs from the water table evaporation rate leaching of pre existing salt crusts and seepage through the lake bottom a reconstruction of the evolution of the palaeosystems through time and space has been attempted with special attention to the instability of the water and ionic balances for different time scales short term fluctuations occurring during a single hydrological cycle annual or seasonal are deduced from the apparent discrepancies between the various indicators found in a given sample long term 10 2 10 3 years changes confirm the existence of a climatic phase being wetter than today from at least ca 9300 and may be from ca 10 900 yr b p to 3000 yr b p for the first time the salinity deduced from diatoms and the 18 o content of the water deduced from that of the carbonate at 25 c are used simultaneously to model the hydrological history of the basins and to estimate the relative humidity of the atmosphere during the holocene major environmental trends recorded from ca 9300 to 3000 yr b p do not show a clear synchronims between the different profiles studied therefore they cannot be interpreted in terms of palaeoclimate but instead demonstrate the importance of local hydrology in the evolution of closed basins associated with groundwater a common situation in arid and semi arid zones

stable isotopes of fossil teeth corroborate key general circulation model predictions for the last glacial maximum in north america 1 oxygen isotope data provide a key test of general circulation models gcms for the last glacial maximum lgm in north america which have otherwise proved difficult to validate high 18o pedogenic carbonates in central wyoming have been interpreted to indicate increased summer precipitation sourced from the gulf of mexico here we show that tooth enamel 18o of large mammals which is strongly correlated with local water and precipitation 18o is lower during the lgm in wyoming not higher similar data from texas california florida and arizona indicate higher 18o values than in the holocene which is also predicted by gcms tooth enamel data closely validate some recent models of atmospheric circulation and precipitation 18o including an increase in the proportion of winter precipitation for central north america and summer precipitation in the southern us but suggest aridity can bias pedogenic carbonate 18o values significantly

paleoelevation reconstruction of the paleocene eocene gonjo basin se central tibet abstract the topography evolution of the southeastern tibetan plateau provides a constraint for evaluating various geodynamic models of plateau formation we reconstruct the paleocene to eocene paleoelevation of the cenozoic gonjo basin in the qiangtang terrane using oxygen and carbon stable isotopic results from pedogenic carbonates of the lower ranmugou formation lithofacies associations indicate that the lower ranmugou formation was deposited in alluvial fan and fluvial floodplain environments u pb dating of volcanics within the middle ranmugou formation constrains the deposition of the lower ranmugou formation as prior to 43 2 ma paleoelevations are calculated using both a thermodynamic model and an empirical relationship the empirical relationship of elevation 18 o is determined from a series of modern water samples calculated paleoelevations indicate that the gonjo basin attained a minimum average elevation of 2100 2500 m in the early eocene together with recent paleoaltimetry studies in the region it can be concluded that the crust of southeastern tibetan plateau was already thickened by that time the calculation is based on the section in northern gonjo basin where 18 o values of paleosol nodules appear to be unaltered but we cannot rule out the possibility that 18 o values of the pedogenic carbonates had been partially reset our preliminary results favor tectonic models compatible with pre miocene uplift of the se central tibetan plateau

pedogenic carbonates forms and formation processes abstract soils comprise the largest terrestrial carbon c pool containing both organic and inorganic c soil inorganic carbon sic was frequently disregarded because 1 it is partly heritage from soil parent material 2 it undergoes slow formation processes and 3 has very slow exchange with atmospheric co2 the global importance of sic however is reflected by the fact that sic links the long term geological c cycle with the fast biotic c cycle and this linkage is ongoing in soils furthermore the importance of sic is at least as high as that of soil organic carbon soc especially in semiarid and arid climates where sic comprises the largest c pool considering the origin formation processes and morphology carbonates in soils are categorized into three groups geogenic carbonates gc biogenic carbonates bc and pedogenic carbonates pc in this review we summarize the available data and theories on forms and formation processes of pc and relate them to environmental factors after describing the general formation principles of pc we present the specific forms and formation processes for pc features and the possibilities to use them to reconstruct soil forming factors and processes the following pc are described in detail earthworm biospheroliths rhizoliths and calcified roots hypocoatings nodules clast coatings calcretes and laminar caps the second part of the review focuses on the isotopic composition of pc 13c 14c and 18o as well as clumped 13c and 18o isotopes known as 47 the isotopic signature of pc enables reconstructing the formation environment the dominating vegetation 13c temperature 18o and 47 and the age of pc formation 14c the uncertainties in reconstructional and dating studies due to pc recrystallization after formation are discussed and simple approaches to consider recrystallization are summarized finally we suggest the most important future research directions on pc including the anthropogenic effects of fertilization and soil management in conclusion pc are an important part of sic that reflect the time periods and formation processes in soils a mechanistic understanding of pc formation is a prerequisite to predict terrestrial c stocks and changes in the global c cycle and to link the long term geological with short term biological c cycles

amount effect recorded in oxygen isotopes of late glacial horse equus and bison bison teeth from the sonoran and chihuahuan deserts southwestern united states stable oxygen isotopes from fossils both vertebrate and invertebrate or inorganic sedimentary minerals frequently have been used to make interpretations about ancient global climates oxygen isotope values measured from terrestrial vertebrates or sedimentary carbonates provide information about paleotemperature and amounts of precipitation at a particular site in general these inferences are made on the centennial to millennial scale serial i e ontogenetic sampling of equus and bison tooth enamel provides climatic data on the scale of months to a few years we present models showing how annual environmental patterns of d 18 o would be replicated in the tooth enamel of equus and bison changes in d 18 o due to shifts in temperature in terrestrial environments d 18 o increases with increased temperature and amount and timing of precipitation increased precipitation may result in a decrease in d 18 o a phenomenon called the amount effect are archived in both equus and bison teeth the input signal is better resolved in bison due to its more rapid enamel growth modeled patterns are compared with actual data from modern sites in the sonoran and chihuahuan deserts of the southwestern united states the isotopic patterns from modern teeth agree with that predicted from known variations in meteoric water known floral and faunal assemblages as well as computer models suggest summer rain for the chihuahuan desert of late glacial time 15 000 10 000 years ago but little summer rain for the sonoran desert at that same time serial data from fossil teeth show a clear pattern interpreted to represent the amount effect that includes increased summer rains in the chihuahuan desert and only minor summer rains in the sonoran desert d 2004 elsevier b v all rights reserved

variations in soil carbonate formation and seasonal bias over 4 km of relief in the western andes 30 s revealed by clumped isotope thermometry abstract carbonate clumped isotope thermometry provides a new method for investigating long standing questions regarding seasonal biases in soil carbonate formation and the relationship between soil carbonate formation temperatures recorded by clumped isotopes t 47 and surface temperatures we address these questions by comparing c o and clumped isotope data from holocene soil carbonates to meteorological and in situ soil monitoring data along a 170 km transect with 4 km of relief in chile 30 s this arid transect experiences a winter wet season and a 20 c range in mean annual air temperature we test the hypothesis that regardless of soil moisture conditions soil carbonates from arid regions record warm season biases and form in isotopic equilibrium with soil water and soil co2 below 3200 m precipitation falls as rain and soil carbonate t 47 values at depths 40 cm resemble summer soil temperatures above 3200 m precipitation falls as snow and t 47 values resemble mean annual soil temperatures soil carbonates from the highest site yield anomalous 18 o 13 c and t 47 values indicative of kinetic isotope effects consistent with cryogenic carbonate formation our findings 1 demonstrate that soil carbonate t 47 values from shallow 40 cm 3 highlight the role of the soil moisture regime in modulating the timing of soil carbonate formation which affects the resulting carbonate t 47 values and 4 show that soil carbonates from high elevation or high latitude sites may form under non equilibrium conditions these findings underscore the importance of understanding past soil moisture conditions when attempting to reconstruct paleotemperatures using carbonate clumped isotope thermometry

stable isotope based paleoaltimetry abstractthe quantitative estimation of paleoaltitude has become an increasing focus of earth scientists because surface elevation provides constraints on the geodynamic mechanisms operating in mountain belts as well as the influence of mountain belt growth on regional and global climate the general observation of decreasing 18o and 2h values in rainfall as elevation increases has been used in both empirical and theoretical approaches to estimate paleoelevation these studies rely on the preservation of ancient surface water compositions in authigenic minerals to reconstruct the elevation at the time the minerals were forming in this review we provide a theory behind the application of stable isotope based approaches to paleoaltimetry we apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations examples of the application of paleoaltimetry techniques to himalaya tibet and the andes are discussed

cenozoic paleoaltimetry of the se margin of the tibetan plateau constraints on the tectonic evolution of the region abstract an improved understanding of the elevation history of the tibetan plateau is crucial in discriminating among the various tectonic models for the evolution of the india asia continental collision we reconstruct the paleoelevation history for three cenozoic sedimentary basins from se tibet and yunnan china to provide more constraints on the tectonic processes for raising the se margin of the tibetan plateau the results presented here together with those of previous studies indicate that 1 the plateau margin of nw yunnan was near its elevation 2 6 km by the latest middle eocene 40 ma 2 the plateau margin of se yunnan reached its current elevation 1 6 km by the middle miocene 13 ma interpretations of the tectonic processes responsible for this inferred surface uplift of the region are made in the context of well documented surface geology we conclude that high landscape 2 6 km elevation in nw yunnan may represent the remnants of the eocene tibetan plateau that originally formed in the northeastern qiangtang block by crustal thickening associated with the india asia continental collision the near modern elevation of se yunnan since 13 ma probably reflects the initiation of lower crustal flow in this area by at least that time collectively our paleoaltimetric interpretations disagree with previously proposed models of middle miocene to pliocene crustal flow acting as a sole tectonic process for raising the se margin of the plateau but support a protracted history of surface uplift that most likely involved crustal thickening during the eocene southeastward extrusion of a portion of eocene tibetan plateau during the oligocene to early miocene and lower crustal flow beneath this region since at least the early miocene

revisiting the equable climate problem during the late cretaceous greenhouse using paleosol carbonate clumped isotope temperatures from the campanian of the western interior basin usa abstract greenhouse climates such as the late cretaceous period provide important reference frames for understanding modern anthropogenic climate change upper cretaceous terrestrial climate proxies have been interpreted as evidence for equable climates with reduced seasonal variations in temperature however climate models have largely failed to reproduce these reconstructions unless parameters such as atmospheric co2 concentrations are set to unreasonable values to help resolve such model proxy disagreements we reconstruct mean annual range in temperature mart for the campanian 75 ma kaiparowits south central utah and two medicine northwest montana formations using warmest mean monthly temperature reconstructions from the clumped isotope composition of paleosol carbonate nodules and reconstructions of local mean annual air temperatures from other methods an evaluation of the applicability of bulk elemental soil geochemistry temperature proxies in these deposits supports the use of previous leaf physiognomy based estimates of mean annual temperature for our mart reconstructions we test the validity of several common assumptions made in reconstructing mart in two novel ways first mart is commonly calculated as twice the difference between local mean annual air temperature and warmest mean monthly temperature and we validate this method by estimating modern mart for a range of environments using climate reanalysis data second we constrain the effect of radiative soil heating on our soil carbonate temperature estimates by showing that for most environments likely to be preserved in the geologic record summer soil temperatures are 9 c larger than previous proxy reconstructions of late cretaceous mart these results add to a growing body of literature showing that terrestrial mart during ancient greenhouse periods was not significantly different from modern seasonal temperature variations finally the similarity in mart between the kaiparowits and two medicine formations suggests that latitudinal changes in mart did not contribute to the faunal provincialism that has been proposed by some paleontologists

combining soil water balance and clumped isotopes to understand the nature and timing of pedogenic carbonate formation abstract pedogenic carbonate is an important archive for paleoclimate paleoecology and paleoelevation studies however it can form under seasonal environmental conditions that differ significantly from the mean growing season environment or mean annual conditions potentially complicating its use for proxy reconstructions the observed seasonal temperature is typically but not always biased high relative to mean annual air temperature mat to evaluate the annual timing of pedogenic carbonate formation ten different soils were sampled across the western united states sites were selected to span a variety of precipitation regimes and soil orders precipitation regimes ranged from arid sites mean annual precipitation map 50 cm dominated by summer precipitation pedogenic carbonate formation temperatures derived from clumped isotope measurements ranged between 6 and 22 c with most samples falling at or below mat clumped isotope temperatures were compared to monthly precipitation normals and modeled monthly values of evapotranspiration and soil water content results show that carbonate formation temperatures agree with the annual timing of soil water depletion suggesting soil moisture content is a primary control on the timing of pedogenic carbonate formation although the seasonal bias is a function of environmental factors that are difficult to reconstruct in paleo studies the use of other paleosol proxies can help to assess if changes in clumped isotope temperatures are a function of changes in air temperature or hydrology these results have important implications for the production of accurate paleoclimate and paleoelevation estimates

an introduction to geosphere biosphere coupling cold seep related carbonate and mound formation and ecology a special session geosphere biosphere coupling cold seep related carbonate and mound formation and ecology was held at the agu fall conference in december 2000 and attracted considerable attention a total of 17 oral presentations were given and some 30 posters were presented this session followed up on discussions which have taken place in the scienti c community over the past few years regarding the role and importance of hydrocarbon seepage and hydrate dissociation in the formation of recently discovered spectacular modern carbonate and mud mounds along the continental margins of the america africa asia and europe these buildups provide an outstanding opportunity to study the processes involved in their formation and provide a challenge in attempting to better understand the coupling between the deep geosphere and the biosphere carbonate mounds were prominent reef types during earth history since cambrian times and these mounds may form giant host rocks for hydrocarbon accumulation carbonate mounds from the geological record provide ample evidence of microbial mediation in mound build up and stabilisation some also suggest an initial control by uid venting advanced models for some palaeozoic mounds argue for the prominent role which bio lms may have played at the interface between the uid and mineral phases while up to the early 1990s there was little evidence of mudmound formation from late cretaceous times onwards recent investigations have increasingly reported occurrences of large mound clusters on modern ocean margins in particular in basins rich in hydrocarbons we should realise that mound provinces are signi cant ocean margin systems up to now largely overlooked how do such recent mound provinces relate to the fossil examples what was and is the role and impact of uid venting on the genesis of large mounds and do the modern mound provinces provide a new window on the microbiota that were instrumental in building giant mounds throughout phanerozoic times these are burning questions and the answers will only come through a new and continuous dialogue between experts of the past explorers of the recent ocean biologists and microbiologists our present day knowledge of reef growth and reef formation is limited to the relatively shallow water reef environments of the tropical regions and to a few observations of reefs from the cool water coral margin oi europe however

oxygen isotope records of goethite from ferricrete deposits indicate regionally varying holocene climate change in the rocky mountain region u s a oxygen isotopes of goethite from ferricrete deposits were measured from both northern and southern rocky mountain localities to assess geographic variability in regional holocene paleoclimate change a f3 7xincrease in oxygen isotope values of 14 c dated goethites in the northern rocky mountains suggests a regional scale relative increase in amounts of isotopically heavy summer precipitation since the early holocene in contrast oxygen isotope values from the southern rocky mountains increase abruptly f2 1xat f6200 14 c yr b p then decrease f2 4xbetween f2000 14 c yr b p and the present we interpret this period of relatively high y 18 o values as evidence for a middle holocene warm period combined with a relatively strong summer monsoon these variable climate records suggest that the rocky mountains of the western united states have had a spatially heterogeneous holocene climate history d 2003 university of washington all rights reserved

paleocene to pliocene low latitude high elevation basins of southern tibet implications for tectonic models of india asia collision cenozoic climate and geochemical weathering the elevation history of the tibetan plateau promises insight into the mechanisms and dynamics that develop and sustain high topography over tens of millions of years we present the first nearly continuous cenozoic elevation history from two sedimentary basins on the southern tibetan plateau within the latest cretaceous to eocene gangdese arc oxygen isotope and 47 clumped isotope compositions of nonmarine carbonates allow us to constrain carbonate formation temperature and reconstruct the paleoprecipitation record of the eocene to pliocene oiyug basin and paleocene to eocene penbo basin we exploit the systematic decrease of surface temperature and meteoric water 18o values with elevation to derive paleoelevation estimates for these basins minimally altered and unaltered pedogenic and lacustrine carbonates from the oiyug basin yield 47 cdes relative to the carbon dioxide equilibrium scale cdes values of 0 625 to 0 755 which correspond to temperatures of 1 30 c using a 47 thermometer for low temperature carbonates similarly the penbo basin yielded 47 cdes values of 0 701 to 0 726 corresponding to temperatures of 6 12 c the apparent evidence for survival of primary clumped isotope values in the face of substantial burial and heating is an important result for the field of carbonate clumped isotope thermometry our paleoelevation estimates for the eocene to pliocene oiyug basin 6 5 4 1 km support previous evidence that high elevations were attained in southern tibet by at least ca 30 ma stable isotope results allow for the possibility of significant topographic subsidence during the miocene as a result of regional extension in the penbo basin our paleoelevation estimates for the paleocene to eocene nianbo formation 4 4 1 3 1 7 km and eocene pana formation 4 1 1 2 1 6 km extend the altitude record of the southern tibetan plateau to pre india asia collision these results support the lhasaplano model of an andean type continental margin tectonic system the rise of the himalayas and tibet is often invoked to understand isotopic proxies for global chemical weathering in the cenozoic and has constrained the debate on the nature of co2 climate weathering feedbacks the nature of the tibetan paleoelevations from pre to postcollision as presented here indicates that high relief at low latitude prevailed on the asian margin much earlier than previously thought thus high topography alone at low latitude is not sufficient to account for the cenozoic weathering proxy record

influence of climate change and uplift on colorado plateau paleotemperatures from carbonate clumped isotope thermometry the elevation history of earth s surface is key to understanding the geodynamic processes responsible for the rise of plateaus we investigate the timing of colorado plateau uplift by estimating depositional temperatures of tertiary lake sediments that blanket the plateau interior and adjacent lowlands using carbonate clumped isotope paleothermometry a measure of the temperature dependent enrichment of 13 c 18 o bonds in carbonates comparison of modern and ancient samples deposited near sea level provides an opportunity to quantify the influence of climate and therefore assess the contribution of changes in elevation to the variations of surface temperature on the plateau analysis of modern lake calcite from 350 to 3300 m elevation in the southwestern united states reveals a lake water carbonate temperature lct lapse rate of 4 2 0 6 c km analysis of miocene deposits from 88 to 1900 m elevation in the colorado river drainage suggests that the ancient lct lapse rate was 4 1 0 7 c km and temperatures were 7 7 2 0 c warmer at any one elevation than predicted by the modern trend the inferred cooling is plausible in light of pliocene temperature estimates off the coast of california and the consistency of lapse rates through time supports the interpretation that there has been little or no elevation change for any of the samples since 6 ma together with previous paleorelief estimates from apatite u th he data from the grand canyon our results suggest most or all of the plateau s lithospheric buoyancy was acquired 80 60 ma and do not support explanations that ascribe most plateau uplift to oligocene or younger disposal of either the farallon or north american mantle lithosphere

clumped isotope paleotemperatures from mis 5 soil carbonates in southern hungary abstract quantitative paleotemperature reconstructions for the continents including east central europe over marine isotope stage 5 mis 5 and specifically the last interglacial lig mis 5e are scarce and mostly based on pollen assemblages here we provide soil and air temperature reconstructions for the summer season of mis 5e 5c using carbonate clumped isotope thermometry applied to soil carbonate concretions in the dunaszekcs loess paleosol record southern hungary the sediments making up the s1 pedocomplex investigated represent the mis 5 as demonstrated by bracketing k feldspar post ir irsl225 290 ages of 63 to 164 ka both the absolute ages and pedogenic susceptibility p curve indicate that all the subtages of mis 5 were found to be recorded in the sequence and soil carbonates found 1 m depth below the paleosurface of the s1 soil provide pristine undisturbed isotopic signals the soil carbonate concretions likely formed during mis 5e at a relatively shallow 20 50 cm depth but a later formation during mis 5c at 50 cm depth is also plausible clumped isotope based soil temperatures st 47sc ranged from 16 to 20 c and reconstructed summer season air temperatures sats for the lig are consistently lower than the modern values at the site by 1 5 c matching surprisingly well the soil bacteria membrane lipid based mis 5e air temperature estimates from a nearby serbian site at the same time the reconstructed sat values do not match the 2 4 c positive warm season anomalies modeled for east central europe between lig and present day in paleoclimate simulations st uncertainties of 1 6 c infiltration driven cooling of soil temperatures and the possibility of mis 5c formation of the investigated carbonates may account for this proxy model data discrepancy oxygen isotope compositions of summer season paleo rainwaters for mis 5e 5c as reconstructed using the st 47sc and 18osc data of soil carbonates were found in a range of 6 7 and 6 4 matching the modern mean summer season value of 6 2 0 94 within error

pedothem carbonates reveal anomalous north american atmospheric circulation 70 000 55 000 years ago our understanding of climatic conditions and therefore forcing factors in north america during the past two glacial cycles is limited in part by the scarcity of long well dated continuous paleoclimate records here we present the first to our knowledge continuous millennial resolution paleoclimate proxy record derived from millimeter thick pedogenic carbonate clast coatings pedothems which are widely distributed in semiarid to arid regions worldwide our new multiisotope pedothem record from the wind river basin in wyoming confirms a previously hypothesized period of increased transport of gulf of mexico moisture northward into the continental interior from 70 000 to 55 000 years ago based on oxygen and carbon isotopes determined by ion microprobe and uranium isotopes and u th dating by laser ablation inductively coupled plasma mass spectrometry this pronounced meridional moisture transport which contrasts with the dominant zonal transport of pacific moisture into the north american interior by westerly winds before and after 70 000 55 000 years ago may have resulted from a persistent anticyclone developed above the north american ice sheet during marine isotope stage 4 we conclude that pedothems when analyzed using microanalytical techniques can provide high resolution paleoclimate records that may open new avenues into understanding past terrestrial climates in regions where paleoclimate records are not otherwise available when pedothem paleoclimate records are combined with existing records they will add complimentary soil based perspectives on paleoclimate conditions

holocene environmental change in the zacapu basin mexico a diatom based record the zacapu basin michoacan mexico is one of a series of internally drained lake basins in the central highlands of mexico the basin has a history of occupation spanning at least 2000 years and before the arrival of the spanish was a major centre for the purepecha culture results are presented of diatom studies from four lacustrine sediment sequences which have holocene radiocarbon dates cemca point 1 cemca point 4 the zacapu core and zacapu section 1 these lie along a transect from the former marsh floor up to the western slopes of the basin zacapu section 1 indicates a deep lake in the basin at some time but the date on this section is thought to be unreliable and the sediments are probably pleistocene in age the other sequences record few major changes in water level in the basin although dry episodes occurred about 4500 bp and more severely about 1000 bp a period of marked catchment disturbance about 7000 to 6000 bp is believed to be the result of volcanic activity on the western flank

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

paleoelevation records from lipid biomarkers application to the tropical andes new results from two novel lipid biomarker based proxies help to constrain the late cenozoic surface elevation history of the eastern cordillera in the tropical northern andes of colombia previous well known studies have suggested rapid latest miocene pliocene 6 3 ma uplift on the basis of an abrupt shift in pollen species assemblages within sedimentary basin fill of the elevated bogota plateau from resampling of these original study localities we provide a revised chronology based on magnetic polarity stratigraphy and we evaluate paleotemperatures using the mbt cbt indices methylation of branched tetraethers cyclization of branched tetraethers and hydrogen isotopic composition d of leaf waxes as two independent proxies of past surface elevation reconstructed paleotemperatures from the mbt cbt proxy show a more gradual cooling trend from ca 7 6 ma to present consistent with less than 1000 m of elevation gain since latest miocene pliocene time and in agreement with geologic evidence for accelerated shortening and exhumation at this time the leaf wax isotopic data on the other hand lack a systematic trend potentially due to fractionation changes associated with uplift induced turnover in floral populations such changes could obscure isotopic variations in meteoric water suggesting that leaf wax isotopic compositions may not provide a direct proxy for elevation in this particular situation involving uplift in a heterogeneous tropical environment more promising in this case is the mbt cbt proxy which may offer a suitable alternative to carbonate based paleoelevation proxies in tropical regions where year round high precipitation rates prevent formation of soil carbonates

high temperature environments of human evolution in east africa based on bond ordering in paleosol carbonates many important hominid bearing fossil localities in east africa are in regions that are extremely hot and dry although humans are well adapted to such conditions it has been inferred that east african environments were cooler or more wooded during the pliocene and pleistocene when this region was a central stage of human evolution here we show that the turkana basin kenya today one of the hottest places on earth has been continually hot during the past 4 million years the distribution of 13c 18o bonds in paleosol carbonates indicates that soil temperatures during periods of carbonate formation were typically above 30 c and often in excess of 35 c similar soil temperatures are observed today in the turkana basin and reflect high air temperatures combined with solar heating of the soil surface these results are specific to periods of soil carbonate formation and we suggest that such periods composed a large fraction of integrated time in the turkana basin if correct this interpretation has implications for human thermophysiology and implies a long standing human association with marginal environments

the evolution of hydroclimate in asia over the cenozoic a stable isotope perspective abstract links between tectonics and regional climate have been extensively studied in asia however despite decades of research the relative roles of tectonics and global climate in pacing the long term evolution of climate in asia remain disputed today climate in asia is characterized by large scale monsoonal circulation over india and southern china and exceptionally arid deserts across much of central asia that to the north yield to the wetter conditions of the steppe and taiga how why and if these boundaries have changed during the cenozoic has been limited by the lack of paleoclimate proxy data that can be broadly applied over space and time we use a large compilation of pedogenic and lacustrine carbonate stable oxygen 18o and carbon 13c isotope data 7 700 samples which record large scale atmospheric circulation and primary productivity respectively to reconstruct cenozoic hydroclimate in asia and delineate the boundaries through time of monsoonal and mid latitude westerly moisture the 18o data indicate that atmospheric circulation has remained similar to today for at least 55 million years southern tibet has always received southerly likely monsoonal moisture and this southerly moisture has likely rarely extended northward of the central tibetan plateau in contrast northern tibet and central asia have received moisture dominantly via the mid latitude westerlies which have maintained a semi arid to arid climate in central asia since the early eocene thus the spatial extent of large scale atmospheric circulation appears largely unperturbed by contemporaneous changes in india asia collisional tectonics extent of the paratethys and in global climate the 13c data support this interpretation but yield additional details particularly low 13c across a wide swath of eastern china during the eocene suggests greater primary productivity due to a strengthened east asia monsoon perhaps driven by high atmospheric pco2 and globally warm temperatures consistently higher 13c in central asia indicates that central asia has remained more arid than surrounding regions such as northern india and southern china which have received abundant precipitation due to the presence of monsoonal moisture however increases in 13c across much of central asia throughout the cenozoic including particularly pronounced increases in mongolia and kazakhstan during the neogene imply that primary productivity has declined across much of asia this large scale de greening is attributable to the combined effects of cenozoic global cooling and the late cenozoic uplift of the tian shan and altai mountains which block westerly moisture the uplift of these ranges in the late miocene is supported by decreasing neogene 18o in eastern kazakhstan and sharply increasing 13c in the lee of the altai these regional data demonstrate that the tian shan and altai reached sufficient elevations to interact with the westerly jet by the late miocene establishing a substantial rain shadow and shifting the seasonality of precipitation in western central asia we conclude that paleoclimatic changes during the cenozoic in central asia are more tightly controlled by global climate and by the interaction of the mid latitude westerlies with the tian shan and altai rather than by changes in the height or extent of the tibetan plateau or paratethys

refining the pedogenic carbonate atmospheric co2 proxy and application to miocene co2 abstract quantifying uncertainty is essential for any paleoenvironmental proxy recent work on propagating error through the equation used to determine atmospheric co 2 concentrations from paleosol carbonates yields conflicting results small magnitude uncertainty from gaussian error propagation contrasts with larger magnitude uncertainty from monte carlo error propagation the discrepancy is reconciled here by revising partial differential equations for the gaussian approach uncertainties calculated using the two approaches are compared and applied to miocene calcic paleosols monte carlo propagated errors are asymmetrical but otherwise agree with gaussian errors three methods for assigning soil respired co 2 concentrations s z to paleosols are also compared a revised calibration of depth to the bk horizon as a direct proxy for s z is presented and although it results in lower atmospheric co 2 concentrations than the original calibration it results in significantly higher calculated atmospheric co 2 than the use of mean annual precipitation as a proxy for s z or assigning s z values based on soil order averaging atmospheric co 2 concentrations calculated using soil order based s z values from 10 penecontemporaenous and independent paleosols will likely result in useful constraints on earth system sensitivity the improvement of proxies for s z is needed to increase the accuracy and precision and to resolve potential volatility in co 2 time series

decline of soil respiration in northeastern tibet through the transition into the oligocene icehouse abstract soil respiration rs the production of carbon dioxide in soils increases dramatically from deserts to forested ecosystems rs values thus provide a potential tool to identify past ecosystems if recorded in sedimentary archives here we propose a quantitative method to reconstruct past rs values from paleosols this method reverses the soil paleobarometer a proxy that estimates past atmospheric co2 concentration values co2atm from paleosols while considering a narrow range of variation for rs we use past co2atm values from marine proxies to reconstruct soil respiration from a 20 million year long isotopic record from northeastern tibet covering the transition from the eocene greenhouse to the oligocene icehouse we show that rs dropped at least 4 fold through the transition into the oligocene icehouse marking the spread of boreal desert steppes of central asia we show that increasing aridity and the decline of monsoonal rainfall in parallel with global cooling caused the fall of soil respiration these highly dynamic rs emphasize the need for a systematic screening of paleosol isotopic data before using the soil paleobarometer to reconstruct co2atm

the clumped isotope geothermometer in soil and paleosol carbonate we studied both modern soils and buried paleosols in order to understand the relationship of temperature t c 47 estimated from clumped isotope compositions 47 of soil carbonates to actual surface and burial temperatures carbonates from modern soils with differing rainfall seasonality were sampled from arizona nevada tibet pakistan and india t c 47 obtained from these soils shows that soil carbonate forms in the warmest months of the year in the late morning to afternoon and probably in response to intense soil dewatering t c 47 obtained from modern soil carbonate ranges from 10 8 to 39 5 c on average t c 47 exceeds mean annual temperature by 10 15 c due to summertime bias in soil carbonate formation and to summertime ground heating by incident solar radiation secondary controls on t c 47 are soil depth and shading site mean annual air temperature maat across a broad range 0 30 c of site temperatures is highly correlated with t c 47 from soils following the equation maat c 1 20 t c 47 0 21 72 r 2 0 92 where t c 47 0 is the effective air temperature at the site estimated from t c 47 the effective air temperature represents the air temperature required to account for the t c 47 at each site after consideration of variations in t c 47 with soil depth and ground heating the highly correlated relationship in this equation should now permit mean annual temperature in the past to be reconstructed from t c 47 in paleosol carbonate assuming one is studying paleosols that formed in environments generally similar in seasonality and ground cover to our calibration sites t c 47 0 decreases systematically with elevation gain in the himalaya following the equation elevation m 229 t c 47 0 9300 r 2 0 95 assuming that temperature varied similarly with elevation in the past this equation can be used to reconstruct paleoelevation from clumped isotope analysis of ancient soil carbonates we also measured t c 47 from long sequences of deeply buried 5 km paleosol carbonate in the himalayan foreland in order to evaluate potential diagenetic resetting of clumped isotope composition we found that paleosol carbonate faithfully records plausible soil t c 47 down to 2 5 4 km burial depth or 90 125 c deeper than this and above this temperature t c 47 in paleosol carbonate is reset to temperatures 40 c we observe 40 c as the upper limit for t c 47 in modern soils from soil depths 25 cm and therefore that t c 47 40 c obtained from ancient soil carbonate indicates substantially warmer climate regimes compared to the present or non primary temperatures produced by resetting during diagenesis if representative this limits the use of t c 47 to reconstruct ancient surface temperature to modestly buried 3 4 km paleosol carbonates despite diagenetic resetting of 47 values 18 o and 13 c values of the same deeply buried paleosol carbonate appear unaltered we conclude that solid state reordering or recrystallization of clumping of carbon and oxygen isotopes can occur in the absence of open system exchange of paleosol carbonate with significant quantities of water or other phases

role of the westerlies in central asia climate over the cenozoic abstract there remains substantial debate concerning the relative roles of tectonics and of global climate in pacing the evolution of aridity in central asia over the cenozoic tibetan plateau uplift variable monsoonal strength paratethys retreat and reduced moisture transport from the north atlantic have all been hypothesized to drive aridity in central asia distinguishing between these mechanisms requires knowledge of moisture transport pathways to central asia through time presently central asia receives recycled high 18 o moisture that has been transported across eurasia by the westerlies while southern tibet receives low 18 o moisture distilled by passage over the himalaya here we reconstruct the spatial distribution of oxygen isotopes in precipitation since the early eocene using a compilation of 18 o data from 2750 sedimentary carbonate samples across asia the spatial distribution of paleo precipitation 18 o remains remarkably similar through time with low 18 o values in the lee of the himalaya in southern tibet constant high 18 o values in central asia and intermediate values on the central plateau despite independent evidence for substantial changes in both topography and climate through time these results suggest that a long standing topographic feature has continuously blocked southerly moisture and subsequent progressive uplift of the tibetan plateau has had little impact on central asian climate in turn southerly monsoonal moisture has never persistently extended northward of the central plateau as a result the westerlies have remained the dominant moisture source in central asia since at least the early eocene therefore sedimentary aridity indicators in central asia such as loess deposition are controlled by the trans eurasian westerly moisture flux rather than tibetan plateau uplift

spatiotemporal distribution of river water stable isotope compositions and variability of lapse rate in the central rocky mountains controlling factors and implications for paleoelevation reconstruction abstract stable isotope based paleoaltimetry is the most widely used approach for paleoelevation reconstruction interpretations of stable isotope data in continental interiors however are undermined by surface water isotope compositions that are influenced by multiple factors here we present a stable isotope dataset of modern river water samples collected over two summers and one spring from the central rocky mountains rockies and the adjacent great plains by examining the spatial and temporal variations of river water 18 o d and d excess values and their relationships with climatic and geographic parameters as well as through back trajectory analysis of moisture sources we elucidate the influences of elevation and climatic parameters on the spatiotemporal variation of river water isotopic values in the bighorn river drainage a typical intermontane drainage in the central rockies the isotopic difference between highland and lowland rivers is small which we attribute to highland precipitation that dominates lowland river discharge in the north platte river drainage across the central rockies and great plains the river water 18 o values show poor correlation with elevation west of 105 w central rockies but increase as elevation decrease east of 105 w in the western great plains this eastward increase across the western great plains leads to an average oxygen isotope lapse rate of 2 3 km which we interpret as being caused primarily by condensation temperature controlled isotopic fractionation at various elevations and secondarily by evaporation in the upper reaches of streams that contribute to the north platte river plus direct contribution of moisture from the gulf of mexico in the great plains in this continental interior setting multiple moisture sources including recycled continental moisture contribute to surface water and evaporation influences river water isotope values to various degrees depending on the relative humidity within an individual river catchment these results suggest that paleoclimate and atmospheric circulation pattern must be carefully evaluated when applying stable isotope based paleoaltimetry in continental interiors our findings have implications for paleoelevation reconstruction in the study area including that 1 within the central rockies the isotopic difference of river water and unevaporated basinal precipitation can be used to infer paleorelief of the laramide ranges with respect to the basin floors 2 along a regional transect crossing the central rockies and great plains the modern isotope lapse rate of the north platte river drainage can be used to constrain the paleorelief between the two regions in semi arid climate

topographic development of the southern alps recorded by the isotopic composition of authigenic clay minerals south island new zealand abstract the southern alps are developing as a consequence of oblique collision between the pacific and australian plates the southern alps lie on the west side of the south island of new zealand and create a massive rain shadow where greater than 12 m year of rain falls on the west coast and semiarid conditions exist to the east the rain out effect across the mountains causes precipitation west of the southern alps to have d and 18 o values averaging 30 and 5 5 whereas precipitation in the rain shadow to the east is isotopically lighter d 72 and 18 o 9 8 such large differences in the isotopic composition of precipitation would not have existed prior to the development of significant topography we have examined the topographic evolution of the southern alps using oxygen isotope analyses of authigenic kaolinites formed in the rain shadow to the east of the mountains between the cretaceous low topography and the pleistocene changes in the isotopic composition of authigenic clay minerals forming in equilibrium with meteoric water in the stratigraphic sequence record the development of southern alps topography and the resultant rain shadow our oxygen isotope analyses of authigenic kaolinites show a 5 6 decrease in the early pliocene from 18 2 in older rocks to 12 3 in younger rocks in addition smectite is abundant in all samples from the late miocene to recent but is conspicuously absent in most older rocks suggesting a change to a generally drier climate roughly coincident with the isotopic shift in kaolinites this method may be useful in unraveling timing of development of mountain belts elsewhere in the world

reconsidering the uplift history and peneplanation of the northern lhasa terrane tibet the elevation history of the tibetan plateau promises insight into the mechanisms and dynamics that develop and sustain high topography over tens of millions of years as well as the contribution of uplift related erosive flux to cenozoic global cooling the elevation history of the center and northern margin of the plateau have been historically less well constrained than the southern margin a diverse suite of techniques each with their own biases and uncertainties yield discrepant mid cenozoic elevation estimates 0 5 km we reconstruct paleogene to miocene elevations of the lunpola basin on the northern lhasa terrane the southernmost crustal block of the tibetan plateau using stable isotope paleoaltimetry and clumped isotope paleothermometry on lacustrine and pedogenic carbonates integrated with previously published compound specific n alkane derived hydrogen isotopes paleo elevation estimates for the lunpola basin 3 1 4 7 km demonstrate that the northern edge of the lhasa block attained high elevation prior to 24 ma and potentially by the early eocene

calibration of the clumped isotope geothermometer in soil carbonate in wyoming and nebraska usa implications for paleoelevation and paleoclimate reconstruction abstract recent work has shown that soil carbonates typically form as the soil dries after seasonal rainfall and therefore record seasonal aspects of climate rather than mean annual conditions because soil carbonate formation is closely related to the timing of local rainfall and drying it is necessary to understand the formation seasonality and temperature and soil water o 18 values recorded in modern soil carbonate before accurate estimates of stable isotope based paleoelevation and paleoclimate can be made here we study carbonate clumped isotope 47 and oxygen isotope o 18 compositions of modern soil carbonates and seasonal variations of soil moisture and temperature of nearby climate stations in wyoming and western nebraska usa to understand the seasonality of soil carbonate formation in semi arid to arid temperate montane settings we find that soil carbonate clumped isotope temperatures t 47 are 3 5 c higher than mean summer air temperature and are similar to or higher than average summer soil temperature at depths 40 cm soil moisture dramatically decreases in early summer following the cessation of spring rains and snowmelt and shows only brief increases after major mid late summer rain events soil water o 18 values calculated using carbonate o 18 and t 47 values are similar to the o 18 values of local mean summer precipitation these lines of evidence suggest that soil carbonates in our study area formed during times of soil dewatering in early summer and after major summer storm events in mid late summer and in or near equilibrium with mean summer precipitation o 18 values t 47 values of modern soil carbonates are inversely correlated with elevation with a lapse rate 4 0 c km similar to the modern air and soil temperature lapse rates calculated soil water o 18 values also are inversely correlated with elevation with a lapse rate of 3 7 km sample elevations can be reconstructed using both t 47 values and calculated soil water o 18 values between 900 m and 2600 m in our studied area with an accuracy of 0 5 km or less however o 18 values of precipitation and soil water reflect the complex interaction of climatic environmental and topographic conditions prior to carbonate formation whereas t 47 values may be influenced by site specific conditions we suggest that both soil carbonate t 47 values and calculated soil water o 18 values should be used to corroborate paleoelevation reconstruction and the seasonal nature of soil carbonate formation should be considered when soil carbonate t 47 values and o 18 values are applied for paleoclimate reconstruction

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

a new approach to stable isotope based paleoaltimetry implications for paleoaltimetry and paleohypsometry of the high himalaya since the late miocene the change in oxygen isotopic composition of precipitation is modeled using equilibrium fractionation during rayleigh distillation linked to the thermodynamics of atmospheric ascent and water vapor condensation the primary controllers of the vertical variation in isotopic composition with elevation are the low elevation temperature and relative humidity as these control the vertical distribution of condensation an empirical fit of precipitation versus model condensation based on alpine stations is derived this fit is represented in the model as the weighted mean composition of condensation within a 1000 m thick air parcel 1500 500 m above the ground surface and is used for all other regions comparison of model versus observed modern precipitation reveals a close fit particularly of more highly elevated sites comparison of modern waters in the himalayas and southern tibet with model predictions particularly as revealed by comparison of observed and predicted hypsometry provides additional support to the validity of the model finally application of this model to estimates of paleo waters in the himalayas and southern tibet reveals that this region had already achieved its present hypsometry by the late miocene about 10 ma ago fl 2001 published by elsevier science b v

seasonal moisture sources and the isotopic composition of precipitation rivers and carbonates across the andes at 32 5 35 5 s collected on both sides of the range in 2002 and 2007 were analyzed we employ a rayleigh isotope fractionation modeling approach to explore spatial and temporal variations in precipitation and river water compositions the results indicate that precipitation on the eastern slopes of the andes at 33s at elevations above 2km is largely derived from a westerly pacific source component and a mixture of easterly and westerly sources below 2km further south at 35s river water compositions exhibit a strong winter influence at 33s rivers have an isotopic minimum of 18 across the core of the range which has an average elevation of 4000m and are topographically offset from similar isotopic values of precipitation by 1000m comparison of precipitation and river water data with temperature corrected d 18 o estimates from pedogenic carbonates illustrates that carbonates capture the range of variability observed in modern precipitation and rayleigh fractionation models

paleoclimatic investigations using isotopic signatures of the late pleistocene holocene groundwater of the stratified aquifers in kuwait abstract the study attempts to determine paleo recharge sources for two major aquifer units of kuwait namely kuwait group aquifer kga and dammam formation dfm were collected and analyzed for major ions and isotopes the obtained results of 14c ages indicated that the groundwater samples ranged from 31 9 ky to 3 9 ky in dfm and 23 3 ky to 0 8 ky in kga the variations in 18o signatures with respect to age reflected that there were two major sources of rainwater such as enriched southern indian ocean monsoon and the depleted northwesterly mediterranean vapor source the samples found to show variations during the three marine isotopic stages mis 1 3 heinrich events bolling allerod and dryas time periods in both aquifers a shift in the intertropical convergence zone itcz was witnessed in the groundwater of both aquifers from 7 8 ky to 4 9 ky the variation in the holocene climate is mainly due to the influence of tropospheric easterly jet governed by the swing in itcz as a result of holocene volcanism the mean 18o values of dfm samples 3 81 reflect depletion than kga samples 2 31 and the d excess values were 0 95 and 2 05 respectively thus it could be inferred that the dfm was predominantly recharged during late pleistocene period and it was in a relatively cooler climate than recharge environment of kga the study infers that kga was recharged between 26on and 26 8on latitudes and that of the dfm was noted to be recharged south west of kuwait in two different patches between 25 8on and 26 2on and 26 7on 27 4on latitudes during late pleistocene the kga was concluded to be recharged between 25 5on and 27 5on latitudes south of kuwait during holocene

loess paleosol carbonate clumped isotope record of late pleistocene holocene climate change in the palouse region washington state usa the channeled scabland palouse region of the pacific northwest pnw of the united states preserves geomorphic and pedosedimentary records that inform understanding of late pleistocene holocene paleoclimate change in a region proximal to the last glacial period cordilleran ice sheet we present a clumped 47 and conventional 18 o 13 c isotopic study of palouse loess paleosol carbonates in combination with carbonate radiocarbon 14 c dating to provide new measures of regional late last glacial 31 20 cal ka bp and holocene soil conditions average clumped isotope temperatures t 47 for last glacial palouse loess paleosol carbonates 9 4 c are significantly lower than those for holocene aged carbonates t 47 18 2 c in study sections calculated soil water 18 o vsmow values 16 2 for last glacial carbonates are also offset relative to those for holocene aged samples 11 1 whereas calculated soil co 2 13 c vpdb values are similar for the holocene 16 9 0 2 and late last glacial 16 7 1 1 periods together these paleoclimate metrics indicate late last glacial conditions of pedogenic carbonate formation in the c 3 grassland soils of the palouse were measurably colder 9 5 c than during the holocene and potentially reflect a more arid last glacial paleoclimate across the palouse findings in agreement with previous proxy studies and climate model simulations for the region

hot or not impact of seasonally variable soil carbonate formation on paleotemperature and o isotope records from clumped isotope thermometry quantifying the timing and temperature of soil carbonate formation is important for interpreting isotopic records of earth surface temperature and soil water composition from paleosols pedogenic carbonates typically have been assumed to form at mean annual temperature but recent work suggests warm season bias in carbonate formation could impact the interpretation of d 18 o values and carbonate

high late miocene pliocene elevation of the zhada basin southwestern tibetan plateau from carbonate clumped isotope thermometry the timing and pattern of tibetan pla teau rise provide a critical test of possible mechanisms for the development and sup port of high topography yet views range widely on the history of surface uplift to modern elevations of 4 5 km to address this issue we present clumped isotope ther mometry data from two well studied ba sins in central and southwestern tibet for which previous carbonate 18 o data have been used to reconstruct high paleoeleva tions from late oligocene to pliocene time clumped isotope thermometry uses mea surements of the 13 c 18 o bond ordering in carbonates to constrain the temperature t 47 and 18 o value of the water from which the carbonate grew these data can be used to infer paleoelevation by exploiting the systematic decrease of surface tempera ture and the 18 o based paleoaltimetry and with paleontological and isotopic data indicating the presence of cold adapted mammals living in a cold high ele vation climate we suggest that late neogene elevation loss across the zhada basin catch ment probably related to local expression of east west extension across much of the south ern tibetan plateau at this time

expansion of c4 grasses in the late miocene of northern pakistan evidence from stable isotopes in paleosols stable isotopic clay mineralogic and bulk chemical analyses were conducted on paleosols of the neogene siwalik sections in northern pakistan in order to reconstruct floodplain environments over the past 17 ma the stable carbon isotopic composition of soil carbonate mean 13c pdb 10 2 and associated organic matter mean 13c pdb 24 1 in paleosols representing 17 7 3 ma reveal that floodplain vegetation was dominated by c3 plants at 7 3 ma a shift toward more positive carbon isotopic values began signaling the gradual expansion of c4 grasses onto the floodplain from 6 ma to present carbon isotopic values for paleosol carbonate mean 13c pdb 0 6 and organic matter mean 13c pdb 14 4 are uniformly enriched in 13c indicating the presence of nearly pure c4 grassland the scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1 0 1 25 m yr or less for the entire 17 ma of record paleosols in the lower portion of the section lack organic a horizons but have reddish b horizons often containing secondary iron oxide nodules leaching depths of soil carbonate in these older paleosols are typically greater than those in the plio pleistocene part of the section where organic a horizons are common and b horizons are markedly more yellow the combined evidence suggests that the mature paleosols in the pre 7 3 ma part of the record are dominantly calcareous alfisols or mollisols that once underlay nearly pure c3 vegetation perhaps trees and shrubs while calcareous mollisols underlying c4 grassland dominate the upper part of the record the carbon and oxygen isotopic trends in the paleosol record in pakistan are also evident in the diet of fossil mammals and in paleosols from nepal thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent wide local effects such as the development or intensification of the asian monsoon driven by uplift of the tibetan plateau may have led to the expansion of c4 grasses if however the expansion of c4 grasses proves globally synchronous then a larger scale cause such as a marked decrease in co2 may be the driving mechanism

paleogeographic and paleotectonic setting of laramide sedimentary basins in the central rocky mountain region in the rocky mountain region between central montana and central new mexico sedimentologically isolated nonmarine basins were produced by basement deformation during the laramide orogeny within the area formerly occupied by a broad late cretaceous foreland basin in which laterally continuous marine facies had accumulated previously laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere laramide basins include perimeter basins along the cratonic periphery of the arcuate laramide province axial basins along a north south intramontane trend and ponded basins located farther west closer to the overthrust belt twelve specific stratigraphic and sedimentologic criteria for the onset duration and termination of laramide deformation allow the chronology of basin development to be inferred independently for each basin maastrichtian initiation of laramide deformation was approximately synchronous throughout the laramide province but termination of laramide deformation was systematically diachronous from north to south between early and late eocene time widespread eocene erosion surfaces truncate syntectonic laramide sequences and are overlain by largely volcanic and volcaniclastic post laramide strata of eocene age in the north and oligocene age in the south fluvial depositional systems draining toward the great plains were dominant in perimeter and axial basins but ponded basins were occupied at times by large lakes that served as regional sediment traps paleocene drainages from ponded basins also led eastward toward the continental interior but partly interconnected lakes that developed within several ponded basins by mid eocene time were either closed hydrologically or else they drained westward into the tyee paleoriver of the pacific northwest

stability of holocene climate regimes in the yellowstone region abstract a 12 500 yr pollen record from loon lake wyoming provides information on the climate history of the southwestern margin of yellowstone national park the environmental reconstruction was used to evaluate hypotheses that address spatial variations in the holocene climate of mountainous regions loon lake lies within the summer dry winter wet climate regime an increase in xerophytic pollen taxa suggests drier than present conditions between ca 9500 and 5500 14 c yr b p this response is consistent with the hypothesis that increased summer radiation and the expansion of the east pacific subtropical high pressure system in the early holocene intensified summer drought at locations within the summer dry winter wet regime this climate history contrasts with that of nearby sites in the summer wet winter dry region which were under the influence of stronger summer monsoonal circulation in the early holocene the loon lake record implies that the location of contrasting climate regimes did not change in the yellowstone region during the holocene the amplitude of the regimes however was determined by the intensity of circulation features and these varied with temporal changes in the seasonal distribution of solar radiation

late cretaceous early eocene laramide uplift exhumation and basin subsidence in wyoming crustal responses to flat slab subduction low angle subduction of the farallon oceanic plate during the late cretaceous early eocene is generally considered as the main driver forming the high rocky mountains in wyoming and nearby areas how the deformation was transferred from mantle to upper crust over the great duration of deformation 40 myr is still debated here we reconstruct basin subsidence and compile paleoelevation thermochronology and provenance data to assess the timing magnitude and rates of rock uplift during the laramide deformation we reconstruct rock uplift as the sum of surface uplift and erosion constrained by combining paleoelevation and exhumation with regional stratigraphic thickness and chronostratigraphic information the amount and rate of rock uplift of individual laramide ranges was less than 2 4 4 8 km 0 21 0 32 mm yr during the early maastrichtian paleocene stage 1 and increased to more than 3 km 0 38 0 60 mm yr during the late paleocene early eocene stage 2 our quantitative constraints reveal a two stage development of the laramide deformation in wyoming and an increase of rock uplift during stage 2 associated with enhanced intermontane basin subsidence exhumation and uplift during stage 1 is consistent with eastward migration of cordilleran deformation associated with low angle subduction whereas the change in exhumation during stage 2 seems to follow a southwestward trend which requires an alternative explanation we here suggest that the increase of rock uplift rate during the late paleocene early eocene and the southwestward younging trend of uplift may be a response to the rollback and associated retreating delamination of the farallon oceanic slab

high elevation of jiaolai basin during the late cretaceous implication for the coastal mountains along the east asian margin abstract a large body of evidence suggests that there were extensive coastal mountains along the east asian margin during the late cretaceous however current knowledge of the paleo mountains the period range and elevation is limited therefore direct paleoaltimetry is needed to validate and evaluate the paleo mountains in east asia our study area is jiaolai basin which is located at the east asian continental margin we estimate the paleoelevation of jiaolai basin during the late cretaceous using carbonate clumped isotope paleothermometry after correcting for seasonal preference latitudinal difference and secular climate change we conclude that the paleoelevation of jiaolai basin was almost certainly 2 0 km at 80 ma combined with the evidence from stratigraphy paleogeography and paleoclimatology our results suggest that the existence of coastal mountains along east asia during the late cretaceous is likely and the model of okhotomorsk east asia collision is preferred

shifts in mid to late holocene anion composition in elk lake grant county minnesota comparison of diatom and ostracode inferences abstract the fossil diatom record from elk lake grant county minnesota was used to reconstruct salinity and brine type between 2640 and 4645 14 c yr bp this lake was selected for a brine type reconstruction because a previous study using fossil ostracode assemblages indicated a shift in anion composition during the mid holocene smith et al 1997 salinity was reconstructed using a transfer function developed for the northern great plains ngp of north america the reconstruction revealed that salinity was higher 1 5 6 2 g l 1 between 4000 and 4645 14 c yr bp and dropped to 0 35 1 2 g l 1 after 4000 14 c yr bp the anion composition of the system was investigated by passively plotting fossil diatom assemblages onto a canonical correspondence analysis cca biplot of the ngp modern samples to determine where core assemblages fell with respect to brine type the biplot suggests that elk lake was mainly a bicarbonate system but temporarily shifted to sulfate domination at 4080 14 c yr bp both the salinity and brine type reconstructions essentially agree with results from smith et al 1997 but the diatom record provides less definitive information on anion proportions as compared to anion concentrations because shifts in the relative abundances of anion associated diatom taxa generally tracked the ostracode inferred changes in brine type we conclude that fossil diatom assemblages can reveal information on shifts in brine type over time and provide insight into brine evolution and groundwater behavior in a lake system

clumped isotope geochemistry the study of naturally occurring multiply substituted isotopologues clumped isotope geochemistry is concerned with the state of ordering of rare isotopes in natural materials that is it examines the extent to which rare isotopes d 13 c 15 n 18 o etc bond with or near each other rather than with the sea of light isotopes in which they swim abundances of isotopic clumps in natural materials are influenced by a wide variety of factors in most cases their concentrations approach within ca 1 relative the amount expected for a random distribution of isotopes deviations from this stochastic distribution result from enhanced thermodynamic stability of heavy isotope clumps slower kinetics of reactions requiring the breakage of bonds between heavy isotopes the mass dependence of diffusive and thermo gravitational fractionations mixing between components that differ from one another in bulk isotopic composition biochemical and photochemical fractionations that may reflect combinations of these simpler physical mechanisms and in some cases other processes we do not yet understand although clumped isotope geochemistry is a young field several seemingly promising applications have already emerged most importantly it appears that proportions of 13 c 18 o bonds in carbonate minerals are sensitive to their growth temperatures independent of bulk isotopic composition thus clumped isotope analysis of ancient carbonates can be used as a quantitative paleothermometer that requires no assumptions about the 18 o of waters from which carbonates grew this approach has been used to reconstruct marine temperatures across the phanerozoic reaching back to the silurian terrestrial ground temperatures across the cenozoic thermal histories of aqueously altered meteorites among other applications clumped isotope geochemistry is also placing new constraints on the atmospheric budget and stratospheric photochemistry of co 2 and should be capable of placing analogous new constraints on the budgets of other atmospheric gases finally this field could be extended to encompass sulfates volatile hydrocarbons organic moieties and other materials

the evolution of latitudinal temperature gradients from the latest cretaceous through the present abstract latitudinal temperature gradients are a defining characteristic of the climate system using thermometric indicators including 18o plant and animal fossils glycerol dialkyl glycerol tetraether gdgt proxies and clumped isotope estimates we document marine and terrestrial temperature gradients for the latest cretaceous late paleocene early eocene early oligocene pliocene and recent the changes in gradients reflect the transition greenhouse to icehouse conditions the evolution of latitudinal temperature gradients in marine and terrestrial realms are similar but has some distinctive differences marine temperatures are generally warmer than those on land except for the late paleocene early eocene the marine records show distinct inflection points at 30 and 50 latitude indicating the existence of frontal systems in the ocean except for the late paleocene early eocene the marine records show an increasingly steeper trend from latest cretaceous through recent being most pronounced after the early oligocene greenhouse icehouse transition this trend reflects the increasing intensity of high latitude and polar cooling as the icehouse state developed during the late paleocene early eocene the oceans were characterized by slightly warmer tropics and much warmer higher latitudes than at present the continents have generally had tropical temperatures like those of today varying by

influence of vegetation type and site to site variability on soil carbonate clumped isotope records andean piedmont of central argentina 32 34 s abstract the clumped isotope geothermometer estimates the formation temperature t 47 of carbonates and has great potential to enhance the extraction of environmental data from pedogenic soil carbonate in the geologic record however the influence of vegetation type and site specific conditions on carbonate formation processes and t 47 records remains poorly understood this study examines the potential for variability in t 47 data between nearby same elevation sites with different c 3 c 4 biomass pedogenic carbonates undercoatings and nodules were collected from five modern soil pits in the semi arid eastern andean piedmont of argentina under a summer precipitation regime three pits were instrumented with temperature and moisture sensors to 1 m depth and a fourth was instrumented with additional soil co 2 and atmospheric temperature relative humidity insolation and rainfall sensors t 47 values mean 30 6 c 1se are invariant with depth and are statistically indistinguishable between the four instrumented sites though a 10 c difference between our t 47 values and those of a nearby peters et al 2013 epsl study suggests the potential for significant site to site variability likely due to local soil hydrology the results of this study suggest that deeper 40 cm t 47 values are consistent with carbonate formation during the early part of soil drying immediately after large mid summer rainstorms carbonate formation 40 cm depth may be biased to soil drying after small frequent precipitation events occurring throughout the spring summer and fall months averaging to shallow summer t 47 values and resulting in a near isothermal t 47 profile

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

hot summers in the bighorn basin during the early paleogene during the early paleogene climate in continental interiors is thought to have been warmer and more equable than today but estimates of seasonal temperature variations during this period are limited global and regional climate models of the paleogene predict cooler temperatures for continental interiors than are implied by proxy data and predict a seasonal range of temperature that is similar to today here we present a record of summer temperatures derived from carbonate clumped isotope thermometry of paleosol carbonates from paleogene deposits in the bighorn basin wyoming united states our summer temperature estimates are 18 c greater than mean annual temperature estimated from analysis of fossil leaves when coupled these two records yield a seasonal range of temperature similar to that in the region today with winter temperatures that are near freezing these data are consistent with our high resolution climate model output for the early eocene in the bighorn basin we suggest that temperatures in continental interiors during the early paleogene greenhouse were warmer in all seasons but not more equable than today if generally true this removes one of the long standing paradoxes in our understanding of terrestrial climate dynamics under greenhouse conditions

examining the spatial consistency of palaeosol proxies implications for palaeoclimatic and palaeoenvironmental reconstructions in terrestrial sedimentary basins terrestrial sediments are a significant archive of past conditions and the critical zone in particular is important for understanding past and ongoing interactions between the atmosphere biosphere and lithosphere understanding the details of a palaeolandscape or palaeocatena record can greatly improve palaeoenvironmental descriptions and palaeoclimate reconstructions during crucial time periods in the past this article presents multi proxy data including palaeosol descriptions major element geochemistry magnetic composition and stable isotope geochemistry from an early eocene palaeosol transect which show distinct trends in palaeosol features and geochemistry across the landscape particularly in terms of the differences between a horizon and b horizon samples a horizon geochemical and physical features are highly variable and reflect other not strictly pedogenic controls whereas b horizon composition is extremely consistent given that most palaeoclimatic or palaeoenvironmental proxies based on palaeosols use b horizon features these results highlight the robustness of those proxies at the same time the difference between a horizons and b horizons and the variability within a horizons of the same palaeosol in different geomorphic settings underscores the importance of palaeosol description detailed sampling and a multi proxy approach to produce both precise and accurate reconstructions of past environments and climates using terrestrial sedimentary records

paleoelevation reconstruction using pedogenic carbonates paleoelevation reconstruction using stable isotopes although a relatively new science is making a significant contribution to our understanding of the recent growth of the world s major orogens in this review we examine the use of both light stable isotopes of oxygen and the new clumped isotope 47 carbonate thermometer in carbonates from soils globally the oxygen isotopic composition 18 o of rainfall decreases on average by about 2 8 km of elevation gain this effect of elevation will in turn be archived in the 18 o value of soil carbonates and paleoelevation can be reconstructed provided 1 temperature of formation can be estimated 2 the effects of evaporation are small 3 the effects of climate change can be accounted for and 4 the isotopic composition of the carbonate is not diagenetically altered we review data from modern soils to evaluate some of these issues and find that evaporation commonly elevates 18 o values of carbonates in deserts an effect that would lead to underestimates of paleoelevation some assessment of paleoaridity using qualitative indicators or carbon isotopes from soil carbonate is therefore useful in evaluating the oxygen isotope based estimates of paleoelevation sampling from deep 50 cm in paleosols helps reduce the uncertainties arising from seasonal temperature fluctuations and from evaporation the new clumped isotope 47 carbonate thermometer expressed as 47 offers an independent and potentially very powerful approach to paleoelevation reconstruction in contrast to the use of 18 o values nothing need be known about the isotopic composition of water from which carbonate grew in order to estimate of temperature of carbonate formation from 47 values using assumed temperature lapse rates with elevation paleoelevations can thereby be reconstructed case studies from the andes and tibet show how these methods can be used alone or in combination to estimate paleoelevation in both cases the potential for diagenetic alteration of primary carbonate values first has to be assessed clear examples of both preservation and alteration of primary isotopic values are available from deposits of varying ages and burial histories 47 values constitute a relatively straightforward test since any temperature in excess of reasonable surface temperatures points to diagenetic alteration for 18 o values preservation of isotopic heterogeneity between different carbonate phases offers a check on diagenesis results of these case studies show that one area of south central tibet attained elevations comparable to today by the late oligocene whereas 2 7 0 4 km of uplift occurred in the bolivian altiplano during the late miocene

stable and clumped isotopes in desert carbonate spring and lake deposits reveal palaeohydrology a case study of the lower jurassic navajo sandstone south western usa

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

diatom based transfer functions for inferring past hydrochemical characteristics of african lakes abstract a new dataset of 282 modern diatom samples and associated environmental information has been created by merging existing regional datasets from north and east africa and niger the relationships between diatom species distributions and hydrochemistry are examined using canonical correspondence analysis cca and partial cca variables reflecting water conductivity ph and cation and anion composition account for significant and independent components of the total variation in the diatom data predictive models transfer functions are developed using the method of weighted averaging for conductivity r 2 0 87 ph r 2 0 77 and ratios between alkali and alkaline earth metals r 2 0 81 and carbonate bicarbonate and sulphate chloride ions r 2 0 82 prediction errors are estimated using the computer intensive method of jackknifing these transfer functions enlarge the potential domain for reconstruction of past hydrochemistry from fossil diatoms preserved in lake sediments

century scale paleoclimatic reconstruction from moon lake a closed basin lake in the northern great plains estimates of past lake water salinity from fossil diatom assemblages were used to infer past climatic conditions at moon lake a climatically sensitive site in the northern great plains a good correspondence between diatom inferred salinity and historical records of mean annual precipitation minus evapotranspiration p et strongly suggests that the sedimentary record from moon lake can be used to reconstruct past climatic conditions century scale analysis of the holocene diatom record indicates four major hydrological periods an early holocene transition from an open freshwater system to a closed saline system by 7300 b p which corresponds with a transition from spruce forest to deciduous parkland to prairie and indicates a major shift from wet to dry climate a mid holocene period of high salinity from 7300 to 4700 b p indicating low effective moisture p et a transitional period of high salinity from 4700 to 2200 b p characterized by poor diatom preservation and a late holocene period of variable lower salinity during the past 2 200 yr indicating fluctuations in effective moisture

spatial variations of holocene climatic change in the yellowstone region abstract the paleoecologic record of the northern rocky mountains shows considerable spatial variability which has been difficult to explain as a unified response to large scale changes in effective moisture or temperature through time comparison of past and present climatic patterns suggests that the spatial heterogeneity in the fossil record arises from a local response to the effects of greater summer solar radiation during the early holocene solar radiation directly determines evapotranspiration and indirectly controls the strength of the summer monsoon and the eastern pacific subtropical high pressure system the yellowstone region provides an example of an area where the indirect effects of solar radiation are manifest by the juxtaposition of two contrasting climatic regimes today and where these regimes were amplified during the early holocene fossil pollen data suggest that central and southern yellowstone the summer dry area became drier in the early holocene while northern yellowstone the summer wet area became wetter the boundary between regimes however is controlled by topography and has not changed significantly in the holocene the spatial variations of holocene vegetation and climatic changes in the northern rocky mountains may therefore be explained as a trade off between strengthened monsoonal circulation and a stronger subtropical high in the early holocene and the relative importance of these precipitation regimes on a topographically complex landscape

ground water processes controlling a prairie lake s response to middle holocene drought lake response to climate forcing is commonly regarded as being controlled by within lake processes we present a case from the northern great plains in which holocene drought response recorded in lake sediments was determined by changes in chemical characteristics of source ground water middle holocene ostracode assemblages were dominated by halophylic limnocythere staplini indicating increased lake water salinity yet the oxygen isotope values in this period decreased by 2 to 3 contrary to expectations of evaporative dominance we infer from these proxy records and ground water flow model results that the paleoclimatic record in the lake was mediated by changes in ground water catchment area and by reduction in evapotranspiration accompanying desiccation of peripheral lake basins

rapid middle eocene temperature change in western north america abstract eocene hyperthermals are among the most enigmatic phenomena of cenozoic climate dynamics these hyperthermals represent temperature extremes superimposed on an already warm eocene climate and dramatically affected the marine and terrestrial biosphere yet our knowledge of temperature and rainfall in continental interiors is still rather limited we present stable isotope 18o and clumped isotope temperature 47 records from a middle eocene 41 to 40 ma high elevation mammal fossil locality in the north american continental interior montana usa 47 paleotemperatures of soil carbonates delineate a rapid 9 11 c temperature excursion in the paleosol record 47 temperatures progressively increase from 23 c 3 c to peak temperatures of 32 c 3 c and subsequently drop by 11 c this hyperthermal event in the middle eocene is accompanied by low 18o values and reduced pedogenic carbonate concentrations in paleosols based on laser ablation u pb geochronology of paleosol carbonates in combination with magnetostratigraphy biostratigraphy stable isotope and 47 evidence we suggest that this pronounced warming event reflects the middle eocene climatic optimum meco in western north america the terrestrial expression of northern hemisphere meco in western north america appears to be characterized by warmer and wetter sub humid conditions compared to the post meco phase large and rapid shifts in 18o values of precipitation and pedogenic caco3 contents parallel temperature changes indicating the profound impact of the meco on atmospheric circulation and rainfall patterns in the western north american continental interior during this transient warming event

caco3 recrystallization in saline and alkaline soils abstract are desert ecosystems a stable sink for atmospheric co 2 although the uptake of atmospheric co 2 by soil during the nighttime is detected in deserts and some semi deserts the underlying mechanisms remain elusive in order to determine the factors affecting the co 2 fluxes into soil and to reveal the relationship between co 2 fluxes and carbonate formation and recrystallization in saline and alkaline soils four soils with contrasting salinity from two sites aksu and yingbazar along the tarim river were analysed soils were incubated in 14 co 2 labelled atmosphere for 90 days at three co 2 concentrations 0 04 0 4 and 4 the 14 c activity was measured in soil water and air as well as in carbonates after 2 14 and 90 days the 14 c incorporation in caco 3 increased with corresponding 14 c decrease remaining in the co 2 the highest 14 c incorporation into caco 3 54 was observed in the yingbazar saline soil the carbonate recrystallization rates increased logarithmically r 2 0 97 with the co 2 concentration the average carbonate recrystallization rate from three sampling times was highest in the yingbazar saline soil under 4 co 2 8 45 10 6 day 1 and lowest in the aksu alkaline soil under 0 04 co 2 0 03 10 6 day 1 the average carbonate recrystallization rate increased with electric conductivity corresponding to soil salinity but decreased with ph r 2 0 99 for 4 co 2 the alkaline soils incorporated less 14 c into caco 3 than the saline soils at the highest co 2 concentration of 4 the full recrystallization period of the remaining primary carbonates was 10 to 100 fold shorter than at the lower co 2 concentrations therefore besides soil chemical parameters e g ph caco 3 content co 2 concentration respiration of microorganisms and roots is an important factor for caco 3 recrystallization and formation of pedogenic carbonates in desert soils it is the most important factor for caco 3 recrystallization and so for the formation of pedogenic carbonates

depositional environment sediment provenance and oxygen isotope paleoaltimetry of the early paleogene greater green river basin southwestern wyoming u s a depositional process sediment provenance and paleotopography are critical to paleogeographic reconstruction during the coeval laramide and sevier orogenies in the cordillera orogenic system here we conduct lithofacies analysis sediment provenance and paleoelevation studies in the fluvial lower paleogene fort union and the main body of the wasatch formations in the center of the greater green river basin in order to reconstruct paleogeography the depositional environment changed from low energy floodplains and associated meandering river during the paleocene to braided rivers during the earliest eocene the lowermost eocene strata have more precambrian basement derived feldspar grains compared to the paleocene strata this change in sediment provenance was associated with the change to dominant northwestward paleoflow direction suggesting major uplift of the laramide uinta mountains during the earliest eocene the 18o values of authigenic carbonates were stable during the early paleocene but decreased gradually from 10 permil during the late paleocene to 18 permil during the earliest eocene suggesting the lack of highland precipitation in the basin catchment during the early paleocene and significant surface uplift and arrival of highland precipitation from the uinta mountains during the earliest eocene the reconstructed paleoelevation of the uinta mountains was at least 3 km possibly greater than 3 5 km and the paleoelevation of the greater green river basin floor was at most 1 km and the paleorelief between the greater green river basin and uinta mountains was 2 km during the earliest eocene our record of the earliest eocene establishment of high topography of the uinta mountains through renewed uplift is 4 to 6 myr older than previously thought if the carbonate cements in the fort union formation record the isotope compositions of surface water from the sevier orogen their high 18o values likely suggest that the sevier orogen had rugged topography during the paleocene

early holocene limnological and climatic variability in the northern great plains information on the timing and direction of climatic and environmental change on a millennial scale exists for many regions of north america whereas little is known about decadal to centennial scale variability here we present a high resolution analysis of diatom inferred salinity from a site in the northern great plains to reconstruct multidecadal and centennial scale climatic patterns during the early holocene the diatominferred salinity indicates a transition from fresh to highly saline conditions between c 13 400 and 7700 cal yr bp which suggests a major shift in climate from wet to dry conditions the overall trend toward increasing salinity is interrupted by several freshwater intervals between c 9800 and 7950 cal yr bp which may be the result of an increase in the frequency of monsoonal flow from the gulf of mexico the early holocene is considered to be a time of rapid change in climate and vegetation within the holocene although rates of change in the moon lake diatom assemblages were hi

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

prolonged high relief in the northern cordilleran orogenic front during middle and late eocene extension based on stable isotope paleoaltimetry the paleoelevation and size of the north america cordilleran orogen during the late cretaceous paleogene contractional and subsequent extensional tectonics remain enigmatic we present new estimates of paleorelief of the northern cordilleran orogenic front during the middle and late eocene using oxygen isotope compositions of unaltered molluscan fossils and paleosol carbonates in the kishenehn basin bounded by several mountains ranges to the east the kishenehn basin was a half graben developed during middle eocene to early miocene collapse of the cordilleran orogen these mollusk taxa include three sympatric groups with affinities to wet tropical semi arid subtropical and temperate environments our reconstructed surface water 18o values vary between 19 8 and 6 3 vsmow during the middle and late eocene the large differences in paleoenvironments and surface water 18o values suggest that the catchment of the kishenehn basin was at variable elevation the estimated paleorelief between the basin and the surrounding mountains based on both rayleigh condensation model and predictions of eocene precipitation isotope values using an isotope enabled global climate model is 4 km and the basin floor was 1 5 km high this high topography and high relief paleogeography suggest that the cordilleran orogenic front reached an elevation of at least 4 km and the crust thickness may have reached more than 55 km before eocene gravitational collapse we attribute the maintenance of high eocene topography to the combination of an inherited thick crust thermal uplift caused by mantle upwelling and isostatic uplift caused by removing lower lithosphere or oceanic slab

paleosols as indicators of paleoenvironment and paleoclimate paleosols are ancient soils that have been incorporated into the geological record soils form in response to interactions among the lithosphere hydrosphere biosphere and atmosphere so paleosols potentially record physical biological and chemical information about past conditions near earth s surface as a result paleosols are an important resource for terrestrial environmental and climatic reconstructions long standing paleosol research topics include morphology classification and clay mineralogy all of which provide information about pedogenic processes and local paleoenvironments paleosols are also used to infer processes involved in the development of stratigraphic architecture and basin evolution recent paleosol research has introduced semiquantitative and quantitative measures for environmental and chronometric reconstructions that provide insight into major regional to global changes in temperature precipitation and atmospheric pco2 these new proxies focus on morphological and chemi

isotopic evidence for shifts in atmospheric circulation patterns during the late quaternary in mid north america wyoming is now at the eastern margin of westerlies originating in the pacific but in the pleistocene appears to have received moisture from elsewhere possibly the gulf of mexico oxygen isotope ratios of pedogenic carbonate in postglacial terraces correspond to ratios in equilibrium with present meteoric waters which show a strong relation to precipitation seasonality and storm sources in contrast the oxygen isotope ratios of all pre holocene soils are significantly more positive even though the carbon isotope composition of coexisting organic matter suggests that the carbonate formed in temperatures cooler than today the oxygen isotope ratios of paleowaters in mid north america appear to be more useful for identifying past storm sources than for estimating paleotemperatures

pedogenic carbonates archive modern and past precipitation change a transect study from soils and loess paleosol sequences from northern iran abstract stable carbon and oxygen isotope compositions in soil carbonates and in soil organic matter provide insights into paleo climatic conditions especially in arid and semiarid regions where carbonate is abundant in soils we here investigate 13c and 18o isotope composition of bulk carbonate pedogenic carbonate nodules and organic carbon from modern soils developed along a precipitation gradient entisol inceptisol mollisol and alfisol and paleosols formed within loess units in northern iran 13c values of organic carbon in the modern soils ranged from 19 5 in the arid and semiarid regions to 24 in the more humid regions with forest vegetation 13c values of bulk carbonate in the modern soils ranged from 12 1 at the wettest sites to 0 8 at the drier sites and thus a 550 mm increase in precipitation leads to a 11 decrease in 13c values of bulk carbonate in the modern soils 13c values of pedogenic carbonate nodules in the semiarid areas show higher values by 3 4 more than the regions with forest vegetation unlike 13c values of pedogenic carbonate nodules the 18o values of pedogenic carbonate nodules of modern soils in this study did not display pronounced changes across the sections the change in 13c of carbonates and organic carbon is consistent with the present above ground vegetation consisting of a mosaic of habitats with differences in the proportion of c3 and c4 vegetation tending to larger c4 contribution with increasing aridity the 13c values of carbonates coupled with climate data of the region confirm seasonal bias in the formation of carbonate nodules in the modern soils seen in studies elsewhere the 13c values of pedogenic carbonate nodules in the paleosols range from 10 in humid areas to 7 2 in semiarid areas the trends in 13c composition in modern soils are also visible in the 13c composition in the paleosols suggesting that in the foothills of the alborz and iranian loess plateau a precipitation gradient existed also in the last interglacial

qaidam basin paleosols reflect climate and weathering intensity on the northeastern tibetan plateau during the early eocene climatic optimum abstract as an important geological archive paleosols have been widely used in reconstruction of paleoenvironmental and paleoclimatic conditions in this study we undertook detailed analyses of the clay mineralogy and carbon and oxygen isotopic compositions of pedogenic carbonates in a series of 13 paleosol horizons within a fluvial section of the eocene 52 44 ma lulehe formation in the qaidam basin pedogenic smectite and illite smectite i s mixed layer minerals are the predominant clay minerals in the paleosols suggesting that the early eocene paleoclimate of the qaidam basin was strongly seasonal with warm wet summers the high levels of pedogenic smectite production and high atmospheric pco2 reconstructed from soil carbonate nodule 13c mean 7 1 0 8 are consistent with elevated temperatures during the early eocene climatic optimum eeco coeval paleosol carbonate nodules yield estimated paleo surface water compositions 18opsw of 7 9 to 6 0 vsmow which are significantly higher than the 18o value of modern summer precipitation in the qaidam basin the estimated temperature difference 5 0 c cooling implies uplift of the study area by nearly 1000 m to its current average elevation of 3000 m above sea level this paleoelevation estimate agrees with modern meteoric water isotopes of global network of isotopes in precipitation gnip sites in asia in the same elevation range

stable isotope evidence for topographic growth and basin segmentation implications for the evolution of the ne tibetan plateau lithologic magnetostratigraphic and stable isotope records from the neogene xunhua and linxia basins along the tibetan plateau9s northeastern margin suggest that topography in the intervening jishi shan mountain range began to develop between 16 and 11 ma perturbations to local climate patterns resulting from the evolution of local topography are tracked through comparison of stable isotope compositions of calcareous basin fill materials across the jishi shan similarity of isotopic compositions is interpreted to reflect the presence of integrated basins whereas distinct isotopic compositions reflect unique basin hydrologies divergent isotope trends develop between ca 16 and 11 ma and are indicative of hydrologic separation in the adjacent xunhua and linxia basins and increased aridity in the leeward xunhua basin the development of aridity in the lee of the growing topography along the plateau9s northeast margin highlights the importance of evaporative enrichment in this extremely continental setting and explains the presence of anomalously positive 18 o values in modern rainfall our findings add to a growing body of evidence for deformation along the plateau9s north and northeastern margins in the middle to late miocene

seasonal bias in the formation and stable isotopic composition of pedogenic carbonate in modern soils from central new mexico usa in order to better calibrate pedogenic carbonate as a proxy for past environments we compared the stable isotopic composition of soil co 2 soil water and pedogenic carbonate in young soils from central new mexico usa seasonal changes in the 13 c value of soil co 2 the 18 o value of soil water and the soil temperature were monitored to establish the timing of isotopic equilibrium with the carbonate calcite solubility was calculated from measured temperatures and co 2 concentrations in the soil this approach allowed us to determine the conditions associated with pedogenic carbonate formation carbon isotope equilibrium oxygen isotope equilibrium and minimum calcite solubility all occurred simultaneously during warm dry conditions in may 2008 when soil co 2 concentrations were low it is therefore concluded that pedogenic carbonate forms during warm dry periods and does not record mean growing season conditions as typically assumed the seasonal bias in pedogenic carbonate formation may explain the occurrence of pedogenic carbonate in monsoon climates and its absence in regions where annual precipitation is more uniformly distributed the implications of the seasonal bias for stable isotope based paleoenvironmental reconstructions are that paleoelevations may have been previously over or underestimated paleoatmospheric co 2 concentrations likely have been signifi cantly overestimated and pedogenic carbonate provides a c 4 biased record of paleovegetation especially in dry soils

rapid uplift of the altiplano revealed through 13c 18o bonds in paleosol carbonates the elevation of earth s surface is among the most difficult environmental variables to reconstruct from the geological record here we describe an approach to paleoaltimetry based on independent and simultaneous determinations of soil temperatures and the oxygen isotope compositions of soil waters constrained by measurements of abundances of 13 c 18 o bonds in soil carbonates we use this approach to show that the altiplano plateau in the bolivian andes rose at an average rate of 1 03 0 12 millimeters per year between 10 3 and 6 7 million years ago this rate is consistent with the removal of dense lower crust and or lithospheric mantle as the cause of elevation gain

the paleoaltimetry of tibet an isotopic perspective stable isotopes provide a valuable perspective on the timing of elevation change of the tibetan plateau we begin our paper by looking in depth at isotopic patterns in modern tibet we show that the 18 o value of surface waters decreases systematically up the himalayan front in central nepal by about 2 8 km in agreement with the patterns documented and modeled by previous research on the tibetan plateau itself there is no apparent correlation between elevation and the 18 o value of flowing surface waters both surface waters and soil carbonates display a northward increase in 18 o values of about 1 5 north of the himalayan crest even though elevation increases modestly the isotopic increase with latitude reduces the isotope elevation gradient for water in the northernmost plateau to 1 to 2 km carbonates in both soils and lakes form at higher temperatures than assumed by previous studies on the plateau temperature estimates from clumped isotope 47 analyses of modern soil carbonates significantly exceed mean annual air t and modeled maximum summer soil temperatures by 15 8 2 8 and 9 7 2 5 c respectively similarly elevated temperatures best account for the 18 o values observed in modern soil and lake carbonates we recalculated paleoelevations from previous studies on the plateau using both higher formation temperatures and latitude corrected isotopic values with one notable exception our revised model produces paleoelevation estimates very close to previous estimates the exception is the reconstruction from late eocene age deposits at xoh xil for which we calculate elevations that are higher and much closer to the current elevation than previously reconstructed therefore there is no evidence for northward progression through time of tibetan elevation change instead the available but admittedly very scanty evidence suggests that much of tibet attained its modern elevation by the mid eocene a truly robust test of the various geodynamic models of uplift await expansion and replication of isotopic records all across tibet especially in the center and north and for 15 ma

investigating the effect of burial histories on the clumped isotope thermometer an example from the green river and washakie basins wyoming abstract the 47 clumped isotope thermometer has been applied to multiple studies aimed at reconstructing the paleoelevation and paleoclimate of sedimentary basins and paleosol sequences ideally this technique directly preserves the temperature of carbonate formation avoiding any speculation on the composition of surface water from which the carbonate precipitated recently however concerns about post depositional alteration of the 47 isotope signature from the effects of burial and or diagenetic alteration have arisen potentially complicating the application of the 47 clumped isotope thermometer for determining paleo surface temperatures here we investigate the effect of burial history on mass 47 clumped isotope to this purpose we collected samples from the surface and from drill cores in two different areas of the greater green river basin the washakie basin near rock springs wyoming and the green river basin near pinedale wyoming both basins are filled with a thick sequence of eocene lacustrine strata and the thermal histories of both basins are well documented from petroleum prospecting studies clumped isotope 47 compositions were measured from lacustrine micritic limestones with a range of peak burial depths from 1 to 6 5 km for samples from the washakie basin that did not experience burial depths exceeding 2000 meters the measured 47 values vary from 0 623 to 0 684 yielding carbonate formation temperatures consistent with previously hypothesized paleocene eocene surface temperatures in contrast samples from the green river basin collected from greater burial depths demonstrate significantly lower 47 values higher temperatures the consistency of 18o values and lack of cl evidence for recrystallization suggest closed system resetting of the clumped isotope thermometer by either partial solid state re ordering or carbonate reprecipitation during burial the 47 values of the deeply buried samples have been compared to values derived from recrystallization and temperature history reordering models thrms both recrystallization and reordering models are successful at predicting 47 reordering at burial temperatures 100 c these observations from samples collected from a basin with a remarkably well constrained thermal history and geothermal gradient highlight the challenges in elucidating burial histories or diagenetic processes solely from clumped isotopic compositions

a simulation of the last glacial maximum climate using the ncar ccsm the national center for atmospheric research community climate system model ncar ccsm is used in a coupled atmosphere ocean sea ice simulation of the last glacial maximum lgm around 21 000 years ago climate in the tropics the simulation shows a moderate cooling of 3 c over land and 2 c in the ocean in zonal average this cooling is about 1 c cooler than the climap sea surface temperatures ssts but consistent with recent estimates of both land and sea surface temperature changes subtropical waters are cooled by 2 2 5 c also in agreement with recent estimates the simulated oceanic thermohaline circulation at the lgm is not only shallower but also weaker than the modern with a migration of deep water formation site in the north atlantic as suggested by the paleoceanographic evidences the simulated northward flow of antarctic bottom water aabw is enhanced these deep circulation changes are attributable to the increased surface density flux in the southern ocean caused by sea ice expansion at the lgm both the gulf stream and the kuroshio are intensified due to the overall increase of wind stress over the subtropical oceans the intensified zonal wind stress and southward shift of its maximum in the southern ocean effectively enhances the transport of the antarctic circumpolar current acc by more than 50 simulated ssts are lowered by up to 8 c in the midlatitudes simulated conditions in the north atlantic are warmer and with less sea ice than indicated by climap again in agreement with more recent estimates the increased meridional sst gradient at the lgm results in an enhanced hadley circulation and increased midlatitude storm track precipitation the increased baroclinic storm activity also intensifies the meridional atmospheric heat transport a sensitivity experiment shows that about half of the simulated tropical cooling at the lgm originates from reduced atmospheric concentrations of greenhouse gases