the paleocene eocene transition at mead stream new zealand a southern pacific record of early cenozoic global change mead stream in marlborough new zealand exposes a spectacular 650 m thick stratigraphic section of well bedded micritic limestone chert and marl that was deposited on a south pacific upper continental slope from late cretaceous to middle eocene the 200 m upper paleocene lower eocene succession was examined for its lithology bulk carbonate carbon isotopes and assemblages of radiolarians calcareous nannoplankton and foraminifera so that it could be placed into a global context the interval displays several prominent carbon isotope anomalies and is correlated with south pacific radiolarian zones rp5 to rp9 and calcareous nannofossil zones np6 8 to np12 additionally planktic foraminiferal zones p4 to p6b are identified in uppermost paleocene and lower eocene strata mead stream has a near continuous paleocene lower eocene sediment record and three globally significant climate events the late paleocene carbon isotope maximum pcim the initial eocene thermal maximum ietm and the early eocene climatic optimum eeco have obvious expressions the pcim is a 50 m thick interval of biosiliceous micritic limestone in which 13c is 3 the lower part contains two organic rich biosiliceous mudstone units that may represent expansion of an oxygen minimum zone omz during a global increase in marine biological productivity the ietm is a 4 m thick interval in which 13c drops below 1 5 in a pattern seen at other locations the basal 2 4 m is a distinctive recessed marl rich unit that is defined herein as the dee marl the ietm is marked by a rapid decline in the nannoplankton genus fasciculithus short lived occurrences of discoaster cf araneus and morozovella aequa aequa and significant radiolarian faunal turnover owing to impoverished benthic faunas the benthic foraminiferal extinction event bfee is poorly defined the onset of the eeco is marked by a 1 negative 13c excursion a transition from limestone rich to marl rich facies and a marked decrease in radiolarian abundance compacted sedimentation rates vary between 1 4 2 7 cm kyr for upper paleocene lower eocene strata at mead stream although individual beds with average thickness of 10 cm were deposited too fast to directly represent cycles in orbital parameters time series analysis of bed thicknesses suggests that groups of beds may record milankovitch scale periodicity perhaps with a significant obliquity component thus the relative frequency and thickness of marl and limestone beds in this section is shown to be strongly influenced by climatic changes at a wide range of temporal scales from suborbital and orbital cycles to aberrant short term events and long term trends predominance of marl in ietm and eeco intervals indicates that episodes of extreme global warming resulted in reduced oceanic productivity and increased terrestrial discharge in the high latitude southwestern pacific

equatorial aridity in western pangea lower permian loessite and dolomitic paleosols in northeastern new mexico u s a abstract lower permian strata have been extensively cored in the subsurface of the bravo dome field northeastern new mexico analysis of core indicates that these strata consist of conglomeratic and sandy fluvial deposits and volumetrically significant eolian silt loessite fluvial facies dominate the lower half of the study interval and include matrix supported massive conglomeratic debris flow units and laminated arkosic sandstone whereas loessite dominates the upper half of the study section and consists of massive well sorted quartzose siltstone that locally reaches thicknesses as much as 120 m in the greater study region paleosols are present throughout the study interval and consist of protosols and dolosols commonly exhibiting vertic features dolomite that is interpreted to be of pedogenic origin is an unusual but volumetrically significant component in these paleosols paleogeographic reconstructions and paleomagnetic data indicate that these strata accumulated at equatorial 3 8 latitudes but depositional and pedogenic evidence both suggest seasonally wet to markedly arid conditions from early wolfcampian to early leonardian time the loessite covers a substantial area 6000 km2 making this the largest pre cenozoic loess accumulation yet documented this is significant because loess generally suggests arid to semiarid conditions intercalated paleosols in the loessite section record repeated cessation of silt influx coupled with landscape stability which we relate to high frequency oscillation between dry and slightly wetter conditions possibly attributable to glacial interglacial climatic conditions that prevailed at low latitudes at a lower frequency the evolution from a predominance of fluvial to primarily eolian strata in tandem with changes in pedogenic character reflect a long term aridification for the study interval these data corroborate independent inferences of monsoon induced equatorial aridity in western pangea and help constrain the timing of the zonal to monsoonal transition to earliest permian time

pedogenic origin of dolomite in a basaltic weathering profile kohala peninsula hawaii we document stoichiometric dolomite occurring in a nonsaline quaternary soil on the kohala peninsula northwestern hawaii geologic constraints and geochemical and isotopic data confirm that this dolomite is not the result of marine influence or wind blown dust the strontium isotopic composition of the dolomite 87sr 87sr 0 7045 0 7048 is indicative of its derivation primarily from the weathering of basaltic parent material rather than from meteoric water or seawater infiltration of soil waters with elevated mg ca 1 derived from alteration of ferromagnesian minerals such as olivine likely led to dolomitization of early precipitated soil calcite and or to direct dolomite precipitation in the profile this demonstrates that well ordered dolomite can form in a nonmarine environment at temperatures 100 c without undergoing burial diagenesis

long lived mesoscale systems in a low convective inhibition environment part i upshear propagation abstractpart ii of this study of long lived convective systems in a tropical environment focuses on forward tilted downshear propagating systems that emerge spontaneously from idealized numerical simulations these systems differ in important ways from the standard mesoscale convective system that is characterized by a rearward tilted circulation with a trailing stratiform region an overturning updraft and a mesoscale downdraft in contrast to this standard mesoscale system the downshear propagating system considered here does not feature a mesoscale downdraft and although there is a cold pool it is of secondary importance to the propagation and maintenance of the system the mesoscale downdraft is replaced by hydraulic jump like ascent beneath an elevated forward tilted overturning updraft with negligible convective available potential energy therefore the mesoscale circulation is sustained almost entirely by the work done by the horizontal pressure gradient and the kinetic energy available from

distribution and origin of protodolomite from the late miocene pliocene red clay formation chinese loess plateau the pliocene epoch is considered the most recent analog of modern warming because co2 levels were similar to the present to explore the carbonate minerals formed in the warmer pliocene epoch we studied two continuous sections of the red clay formation on the chinese loess plateau clp by x ray diffraction xrd fourier transform infrared spectroscopy ftir scanning electron microscopy sem and stable isotope mass spectrometry the red clay formation on the clp exhibits diagnostic ftir absorption features of calcite and protodolomite this allowed quantification of the two carbonate minerals by the ftir method using the ftir method we estimate the average concentration of protodolomite in bajiazui is 3 6 whereas the duanjiapo section is 6 0 protodolomite occurrence is more consistent and the concentration is higher from similar to 6 5 4 2 ma b p and decreases markedly from 4 2 2 6 ma b p red clay protodolomite is depleted in both delta c 13 pdb and delta o 18 pdb ranging from 4 1 to 10 4 and from 6 7 to 11 6 respectively and has a slightly higher delta o 18 value than the calcites sem observations show that red clay protodolomite is composed of euhedral rhombic crystals that range from 1 20 mu m in diameter grow into the soil voids and coexist with authigenic calcite and palygorskite these observations imply that the protodolomite grew in situ and is authigenic from pedogenesis dolomitization in the red clay sequence appears to be the result of overcoming kinetic barriers we propose that in the red clay a warm climate with seasonal dry conditions leads to the formation of calcrete from soil pore waters thereby enriching the pore solutions with respect to mg2 and significantly increasing the mg ca ratio bringing about the formation of protodolomite

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

the influence of convective thermal forcing on the three dimensional circulation around squall lines abstract midlatitude squall lines are typically trailed by a large region of stratiform cloudiness and precipitation with significant mesoscale flow features including an ascending front to rear flow a descending rear inflow jet line end vortices and at later times mesoscale convective vortices the present study suggests that the mesoscale circulation in the trailing stratiform region is primarily determined by the time mean pattern of heating and cooling in the leading convective line analysis of the line normal circulation shows that it develops as thermally generated gravity waves spread away from the leading line midlevel line end vortices are the result of diabatically driven tilting of horizontal vorticity generated by the time mean thermal forcing in the presence of the coriolis force a symmetric thermal forcing generates an asymmetric stratiform circulation and a pattern of vertical displacement that resembles the comma shaped stratiform anvil observed in real systems this suggests tha

the relationship between emex mesoscale precipitation feature properties and their environmental characteristics abstract characteristics of the prestorm environment of equatorial mesoscale experiment emex mesoscale precipitation features mpfs are related to properties of them systems using regression analysis although environmental thermodynamic parameters are poorly correlated with emex mpf properties mainly because environmental thermodynamic conditions varied little among mpfs kinematic parameters are well correlated to these properties lines whose environments have low level shear the shear between about 950 and 750 mb exceeding 5 m s 1 are oriented normal to the direction of this shear lines where the low level shear is under 5 m s 1 are oriented along the direction of the midlevel shear the shear between about 800 and 400 mb convective line speeds correlate well with the maximum speed of the rear to front flow in the troposphere below 300 mb direction of mpf motion is nearly coincident with the tropospheric mean wind direction convective line length is proportional to the magnitude of the men

the application of cathodoluminescence to interpreting the diagenesis of an ancient calcrete profile a laterally extensive calcrete profile has been identified in the late asbian lower carboniferous shallow marine shelf limestones of the llangollen area north wales the upper surface of the profile is defined by a laterally discontinuous palaeokarstic surface and by laminated calcareous crusts which developed within the underlying limestone the profile contains a unique series of early pore filling vadose cements which only occur down to 1 m below the palaeokarstic surface cathodoluminescence reveals that these cements pre date the late pore filling meteoric phreatic cements which occur throughout local asbian lithologies a spar cement stratigraphy has been established for the calcrete profile subaerial vadose cements comprise two generations of non luminescent cement followed by a brightly luminescent generation which occasionally shows an acicular habit this needle fibre calcite represents the final stage of vadose cementation precipitation of vadose cements was contemporary with subaerial alteration and micritization of the limestone textures visible only with cathodoluminescence provide evidence of recurrent periods of fabric dissolution the most extensive phase of dissolution occurred immediately after the precipitation of the non luminescent subaerial vadose cements several different textures have been recorded each reflecting the morphology of a partially dissolved substrate dissolution textures are generally confined to the walls of the larger pores and to early brecciation fractures these probably acted as fluid pathways in the calcrete during early subaerial diagenesis much of the non marine micrite in the calcrete profile appears as needle fibre calcite under cathodoluminescence this acicular calcite was probably formed in response to localized supersaturation of meteoric pore fluids caused by periods of near surface evaporation since needle fibre luminescence is strongly variable these ambient conditions are not believed to have directly controlled the activator ion concentrations of cementing pore waters needle fibre calcite is considered to be a cement precipitate which has almost completely recrystallized to micrite probably during the late stages of subaerial diagenesis two generations of subaerial micrite which define a micrite stratigraphy have been distinguished under cathodoluminescence reconstructing the diagenetic history of this ancient calcrete profile has revealed that subaerial alteration was multistaged with many diagenetic processes acting simultaneously during a single phase of emergence

an ensemble of convective systems on 11 february 1993 during toga coare morphology rainfall characteristics and anvil cloud interactions abstract an active day during the coupled ocean atmosphere response experiment coare intensive observation period iop is examined in which nine convective systems evolved and moved eastward across the region of shipboard radar coverage in the intensive flux array ifa within westerly wind burst conditions the detailed genesis morphology and interactions between these cloud systems are documented from a radar and satellite perspective one of these systems was a large and complex elliptical cluster among the largest observed during the tropical ocean global atmosphere coare multiple parallel deep convective lines spaced 20 30 km apart and embedded within this system were initially oriented from north northwest to south southeast oblique to the storm motion furthermore the lines underwent counterclockwise realignment as the system moved eastward the influence of strong lower tropospheric directional and speed shear on these convective system properties is examined in the context of a dynamic

piggyback basin in the sevier orogenic belt utah implications for development of the thrust wedge timing data on a frontal thrust system indicate that the sevier thrust wedge of central utah advanced rapidly to its ultimate structural front in 30 m y between early albian and campanian time it then persisted by out of sequence thrusting for an additional 25 m y until the early eocene the key to the history of the frontal thrust is a piggyback basin that formed on the hanging wall unconformity bounded sedimentary units within the basin thin both westward and eastward onto structures generated by thrust faulting up to 860 m of upper campanian to lower eocene strata accumulated between these structures which consist of a ramp anticline in the west and a thrust duplex in the east the newly recognized interaction of coeval deposition and thrust deformation permits revised limits on the inception and longevity of the frontal thrust system

positive feedback drives carbon release from soils to atmosphere during paleocene eocene warming the paleocene eocene thermal maximum petm is the most rapid climatic warming event in the cenozoic and informs us how the earth system responds to large scale changes to the carbon cycle warming was triggered by a massive release of 13c depleted carbon to the atmosphere evidenced by negative carbon isotope excursions cie in nearly every carbon pool on earth differences in these cies can give insight into the response of different ecosystems to perturbations in the carbon cycle here we present records of 13ccc of pedogenic carbonates and 13corg from preserved soil organic matter in corresponding paleosols to understand changes to soil carbon during the petm cies during the event are larger in pedogenic carbonates than preserved organic matter for corresponding paleosols at three sites across two continents the difference in the cies within soil carbon pools can be explained by increased respiration and carbon turnover rates of near surface labile soil carbon increased rates of labile carbon cycling combined with decreases in the amount of preserved organic carbon in soils during the petm suggests a decrease in the size of the soil carbon pool resulting in a potential increase in atmospheric pco2 and a positive feedback with warming the petm is a model for how the earth system responds to warming and this mechanism would suggest that soils might serve as a large source for atmospheric co2 during warming events

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

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

the vertical structure of toga coare convection part i radar echo distributions radar data collected by the 5 cm mit radar which was deployed aboard the r v vickers during the intensive observing period of the tropical ocean global atmosphere coupled ocean atmosphere response experiment are partitioned into convective and stratiform cartesian grid columns the vertical structure of convective echo is examined through the use of two variables echo top height and the height of the 30 dbz reflectivity contour the first of these variables has traditionally been used to describe the vertical structure characteristics of convection and the second has recently been linked to internal microphysical properties and lightning histograms of the relative frequency of convective only echo top heights and 30 dbz contour heights were constructed for the three cruises of the vickers with each cruise experiencing different phases of the intraseasonal oscillation iso cruise 1 which was dominated by the convectively inactive phase of the iso was characterized by the highest frequency of shallow convection based on echo top heights whereas cruise 2 which was dominated by a particularly well defined passage of the convective phase of the iso exhibited the tallest echo top heights cruise 3 convection was influenced by moderate westerly surface winds characteristic of postwesterly wind burst conditions and convection was of intermediate height when viewed as a function of internal vertical structure i e 30 db z contour height the frequency distributions vary less from cruise to cruise with cruises 1 and 2 having nearly identical distributions of convective 30 dbz contour heights furthermore when the contribution to convective rainfall is examined as a function of 30 dbz contour height it is seen that relatively more rain fell from vertically intense convection i e convection with tall 30 dbz contours during cruises 1 and 3 than during cruise 2 instantaneous correlations between rainfall rate and radar echo height were highly scattered about a mean value of about 0 55 whereas rainfall rate and 30 dbz contour height correlations peaked at about 0 8 and exhibited much less scatter

magnitude of the carbon isotope excursion at the paleocene eocene thermal maximum the role of plant community change carbon isotope measurements 13 c of leaf wax n alkanes from the paleocene eocene thermal maximum petm in the bighorn basin wyoming reveal a negative carbon isotope excursion cie of 4 5 which is 1 2 larger than that observed in marine carbonate 13 c records reconciling these records requires either that marine carbonates fail to record the full magnitude of the cie or that the cie in plants has been amplified relative to the marine amplification of the cie has been proposed to result from an increase in available moisture that allowed terrestrial plants to increase 13 c discrimination during the petm leaf physiognomy paleopedology and hydrogen isotope ratios of leaf wax lipids from the bighorn basin however all suggest that rather than a simple increase in available moisture climate alternated between wet and dry during the petm here we consider two other explanations and test them quantitatively with the carbon isotopic record of plant lipids the marine modification hypothesis is that the marine carbonate record was modified by chemical changes at the petm and that plant lipids record the true magnitude of the cie using atmospheric co2 13 c values estimated from the lipid record and equilibrium fractionation between co2 and carbonate we estimate the expected cie for planktonic foraminifera to be 6 instead the largest excursion observed is about 4 no mechanism for altering marine carbonate by 2 has been identified and we thus reject this explanation the plant community change hypothesis is that major changes in floral composition during the petm amplified the cie observed in nalkanes by 1 2 relative to marine carbonate this effect could have been caused by a rapid transition from a mixed angiosperm conifer flora to a purely angiosperm flora the plant community change hypothesis is consistent with both the magnitude and pattern of cie amplification among the different n alkanes and with data from fossil plants this hypothesis predicts that the magnitude and pattern of amplification of cies among different n alkanes will vary regionally and systematically depending on the extent of the replacement of conifers by angiosperms during the petm 2007 elsevier b v all rights reserved

evolution and dynamics of a late stage squall line that occurred on 20 february 1993 during toga coare abstract airborne doppler and flight level data are used to document the structure and evolution of portions of a late stage horseshoe shaped squall line system and its effect on vertical momentum and mass transports this system which occurred on 20 february 1993 during the tropical ocean global atmosphere coupled ocean atmosphere response experiment was similar to many previously studied but had some unique features first a slow moving transverse band which formed the southern leg of the horseshoe drew most of its low level updraft air from the squall line stratiform region on its north side rather than the environment to the south second a long lived cell with many properties similar to a midlatitude supercell formed 150 km to the rear of the squall line this cell was tracked for 4 h as it propagated into and then through the cold pool and finally dissipated as it encountered the convection forming the northern edge of the horseshoe finally as the squall line was dissipating a new con

watershed reconstruction of a paleocene eocene lake basin using sr isotopes in carbonate rocks provenance studies have used sr isotopes 87 sr 86 sr of silicate source rocks as a link to their eroded basinal equivalents this technique however cannot identify the proportional inputs from different watersheds or define more precisely sedimentation events due to tectonic or climatic change erosion of carbonate rocks dominates the sr input within basin drainage and potentially can be used through 87 sr 86 sr ratios to reconstruct paleohydrology of the entire basin and trace watershed inputs and depositional patterns in continental basins the sr isotopic ratios from waters of the source area allowing for the mixing of shallow groundwater and surface water along the transport path are homogenized in the basinal carbonate sediments mineralogy and diagenesis of carbonate rocks generally do not affect the sr isotopic signal in a near surface system lacking external influence by volcanism eolian dust or deep geothermal waters the 87 sr 86 sr ratios from the source area are directly comparable to those in the receiving continental basin the sr isotopic signal of the paleocene eocene flagstaff formation central utah a carbonate lake deposit in a foreland basin is compared to that of projected source waters draining its thrust front the sevier fold thrust belt freshwater carbonates compose a large portion of the lowermost ferron mountain and uppermost musinia peak members of the formation whereas gypsum and carbonates predominate in the middle cove mountain member previous research had attributed gypsum deposition to the deposition of the middle cove mountain member to either climatic change or unroofing of diapirs of jurassic gypsiferous carbonates to examine more closely the influence of climate versus tectonics on flagstaff sedimentation as well as the efficacy of provenance studies using carbonates we collected rock samples from the three members of the formation on the wasatch plateau of central utah in addition to sampling stream water associated with pennsylvanian permian and jurassic carbonate terrains from the nearby thrust front the 87 sr 86 sr ratios in carbonates and gyprock belonging to the flagstaff formation remained unchanged during deposition the average sr isotope composition of the flagstaff rocks being identical to that of sampled waters draining the projected provenance area there was little change in source rock weathering as the thrust front evolved deposition of gypsum occurred in the basinal lake only during the deposition of the middle cove mountain member despite its constant exposure in the drainage area suggesting a changing balance of tectonic and climatic controls during lake sedimentation the 87 sr 86 sr isotopic studies targeting carbonate rocks and their presumed source waters are a simple but accurate method for reconstructing the paleohydrology of lake basins

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

continental paleotemperatures from an early cretaceous dolomitic lake gansu province china abstract the lower cretaceous strata of asia are renowned for abundant fossil resources these strata can also offer a wealth of quantitative data regarding the paleoclimate and paleoenvironment of the terrestrial cretaceous an important transition in earth history many modern groups of organisms that dominate terrestrial ecosystems today originated or expanded in the early cretaceous in addition the cretaceous period known to have been characterized by a greenhouse climate provides opportunities to understand how the climate system functioned during greenhouse climate states here we utilize the clumped isotope paleothermometer to provide paleotemperature records from a lacustrine sequence in northwestern china previously constrained to the early aptian petrographic and x ray diffraction analyses indicate that the lake sediments produced primary to early diagenetic dolomites likely microbially mediated due to high organic matter input and seasonally warm arid conditions the majority of the dolomitic carbonates formed in pore waters just below the sediment water interface or as primary shallow water precipitates clumped isotope derived temperatures from all carbonates range from 20 6 c for early diagenetic dolomites to 47 2 c for late burial calcite cements accounting for seasonal biases mean annual air temperatures are calculated to have averaged 20 2 c this is broadly consistent with local paleotemperature proxy evidence and climate model paleotemperature estimates the data presented provides further quantitative constraints on the cretaceous greenhouse world as well as insights into depositional settings that produce low temperature dolomites

the cenozoic climatic and topographic evolution of the western north american cordillera herein we present oxygen isotope records from cretaceous to recent terrestrial sediments in the western north american cordillera the purpose of this analysis is to use oxygen isotope records to understand the coupled surface elevation and climate histories of this region through the cenozoic to do this we constructed 18o maps of surface waters for time intervals that trace the development of topography of western north america these maps are based on 4861 oxygen isotope analyses from both published 4478 and new 383 data we determined the 18o values of surface waters using paleotemperatures derived previously from floral assemblages and the appropriate isotope fractionation factors these data suggest that in the late cretaceous to early eocene the sevier hinterland formed a plateau of unknown height around 50 ma a topographic wave developed in british columbia and eastern washington that swept southward reaching northeastern nevada at 40 to 38 ma and southern nevada 23 ma this southward encroachment of an eocene plateau sweep caused reorganization of drainage patterns such that the intraforeland basins of wyoming and utah drainages extended deep within the sevier hinterland as the wave swept southward the landscape within the sevier hinterland developed into a rugged and high mountain range with the hypsometric mean elevation of 4 km and relief of 1 5 km this eocene highland was bordered on the west by a high sierra nevada ramp and on the east by the intraforeland basins that captured water draining these growing highlands the spatial and temporal evolution of this highland correlates with the timing of volcanism and extension these observations support tectonic models that call for north to south removal of the farallon slab or piecemeal removal of mantle lithosphere the isotopic data show that prior to growth of this highland the north american monsoon nam penetrated much farther north in the paleocene eocene than today the combined effects of global cooling increasing latitudinal temperature gradients and the generation of the orographic barrier created by the growing north to south highland produced a southward migration of the nam front by the oligocene the hydrologic regime that we observe today was in place it has been modified since then as a result of basin and range extension and collapse of the highlands in the mid miocene this collapse allowed the nam to penetrate farther north into the great basin of nevada and utah

warm not super hot temperatures in the early eocene subtropics the early eocene ca 55 48 ma encompasses one of the warmest intervals of the past 65 m y and is characterized by an unusually low equator to pole thermal gradient recent proxy studies suggest temperatures well in excess of 30 c even at high latitudes but confl icting interpretations derived from different types of data leave considerable uncertainty about actual early eocene temperatures a robust comparison among new paleotemperature proxies may provide insight into possible biases in their temperature estimates and additional detail on the spatial distribution of temperatures will further resolve the early eocene meridional temperature gradient we use a suite of paleotemperature proxies based on the chemistry of bivalve shell carbonate and associated sedimentary organic matter from the united states gulf coastal plain to constrain climate at a subtropical site during this key interval of earth history oxygen isotope and clumped isotope analyses of shell carbonate and two tetraether lipid analyses of sedimentary organic carbon all yield temperatures of 27 c high resolution intraannual oxygen isotope data reveal a consistent large range of seasonal variation but clumped isotope data suggest that seasonality is due primarily to precipitation not to temperature these paleotemperature estimates are 2 3 c warmer than the northern gulf of mexico today and generally consistent with early eocene temperature estimates from other low and mid latitude locations but are signifi cantly cooler than contemporaneous estimates from high southern latitudes

upscale evolution of mcss doppler radar analysis and analytical investigation abstract the development of two small mesoscale convective systems mcss in northeastern colorado is investigated via dual doppler radar analysis the first system developed from several initially isolated cumulonimbi which gradually coalesced into a minimal mcs with relatively little stratiform precipitation the second system developed more rapidly along an axis of convection and generated a more extensive and persistent stratiform echo and mcs cloud shield in both systems the volumetric precipitation rate exhibited an early meso scale convective cycle a maximum and subsequent minimum followed by reintensification into a modest mature stage this sequence is similar to that noted previously in the developing stage of larger mcss by mcanelly and cotton they speculated that the early meso convective cycle is a characteristic feature of development in many mcss that is dynamically linked to a rather abrupt transition toward mature stage structure this study presents kinematic evidence in suppo

gravity wave influences on mesoscale divergence an observational case study characteristics of tropospheric low frequency gravity waves are diagnosed in radiosonde soundings from the tropicalwarm pool international cloud experiment near darwin australia the waves have typical vertical wavelengths of about 4 km horizontal wavelengths of about 600 km and intrinsic periods of about 12 hr these scales match those of the vertical horizontal and temporal variability found in area averaged horizontal wind divergence over the same domain vertical profiles of divergence show wave like structures with variability of the order of 2 10 5 s 1 in the free troposphere the results for darwin are similar to previously reported observed mesoscale patterns of divergence convergence over the tropical atlantic the findings imply that tropical divergence on spatial scales of a few hundred kilometers which is known to influence the organization of convection may be forced by gravity waves

secondary initiation of multiple bands of cumulonimbus over southern britain ii dynamics of secondary initiation summary the convective storm initiation project csip pilot field programme took place in the summer of 2004 in southern england during this field campaign a case of a cold pool outflow initiating an arc of convection downwind of the generating storm the primary storm was observed three further arcs were initiated further downwind of this first arc these arcs all later gave significant rainfall over south east england results from the modelling studies described in this paper show that gravity waves generated by the primary storm may have been responsible for initiating the further three arcs of convective showers that were observed the modelled primary storm generates waves with a range of vertical wavelengths these are separated by dispersion with the higher order modes with the largest vertical wavelengths travelling fastest approximately 30 m s 1 the fastest two modes suppressed convection and later modes increased boundary layer depth and so initiated convection the multiple peaks from non hydrostatic effects in the third mode may have been responsible for the two main arcs observed and the fourth mode may have been responsible for the third arc the amplitude of the modelled waves at low levels was much larger downwind of the primary storm than upwind and only initiated convection there which agrees with the observations of the arcs forming downwind of the primary storm this asymmetry appears to be caused by the moving wave source and asymmetric wave trapping finally we discuss the implications for numerical weather prediction nwp reducing the resolution of the model and varying the magnitude of the wind speed used shows that a non hydrostatic high resolution 1k m nwp model should be able to capture such wave processes if the generating storm is forecast or analysed correctly

a numerical investigation of the organization and interaction of the convective and stratiform regions of tropical squall lines abstract a set of 13 two dimensional numerical simulations based on the 22 and 23 june soundings from the convectionprofonde tropicale in 1981 copt81 experiment in west africa is used to study the organization and interactionof the convective and stratiform regions of squall line type convective systems the initial wind profiles arecharacterized by the african easterly jet aej and the tropical easterly jet tej located at about 3 5 km and14 km respectively the physical processes that generate and maintain the mesoscale inflow at the rear of squall line type mesoscaleconvective systems are thereby examined horizontal potential temperature gradients generated by a combinationof latent heat release in the convective region and unsaturated mesoscale descent both modulated by evaporation cause a horizontal pressure gradient and generate horizontal line parallel vorticity the rear inflow is a consequenceof these processes the convective activity induces a significant upscale influence ahead of the

formation of dolomite at 40 80 c in the latemar carbonate buildup dolomites italy from clumped isotope thermometry the temperature of formation of replacement dolomite and 18 o h 2 o of dolomitizing fluid in the latemar carbonate buildup dolomites italy were estimated independently from carbonate clumped isotope thermometry dolomite formed at 42 72 9 11 c 2 standard deviations sd from fluid with 18 o h 2 o that averages 0 3 3 3 vienna standard mean ocean water 2 sd the estimated temperature and 18 o h 2 o are similar to those of modern diffuse flow fluids at mid ocean ridges the kind of fluid that has been proposed previously as the dolomitizing fluid in the latemar buildup based on the trace element compositions of dolomite calcite in limestone preserves original 18 o but records clumped isotope temperatures 44 76 9 11 c 2 sd that are higher than those at which the limestone formed temperature recorded by calcite but not 18 o was likely reset during dolomitization clumped isotope thermometry has great potential for application to studies of burial and diagenesis by retrieving independent estimates of temperature and 18 o h 2 o with uncertainties as low as 5 c 2 standard errors se and 0 75 2 se respectively from a single stable isotope analysis of a carbonate mineral

numerical simulation of a midlatitude squall line in two dimensions abstract a two dimensional anelastic cloud model was used in attempts to numerically replicate the observed structure of a midlatitude squall line initial conditions were adapted from observations of the 22 may 1976 oklahoma line model simulations were made with and without considering the ice phase of water these model storms have within the constraints of the model s geometry replicated the basic multicellular character and general line normal airflow typical of these lines in addition the structure and intensity of the subcloud cold air pool and the propagation speeds developed by the storms appear to be reasonable further it was found that the initial conditions chosen resulted in model storms which were not only long lasting but also essentially repetitive indicating that a state of quasi equilibrium had been attained the storms did not decay because the environmental conditions ahead of the storms were favorable and essentially unchanged during the course of the simulations the inclusio

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

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

the role of environmental shear and thermodynamic conditions in determining the structure and evolution of mesoscale convective systems during toga coare abstract a collection of case studies is used to elucidate the influence of environmental soundings on the structure and evolution of the convection in the mesoscale convective systems sampled by the turboprop aircraft in the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare the soundings were constructed primarily from aircraft data below 5 6 km and primarily from radiosonde data at higher altitudes the well documented role of the vertical shear of the horizontal wind in determining the mesoscale structure of tropical convection is confirmed and extended as noted by earlier investigators nearly all convective bands occurring in environments with appreciable shear below a low level wind maximum are oriented nearly normal to the shear beneath the wind maximum and propagate in the direction of the low level shear at a speed close to the wind maximum when there is appreciable shear at middle levels 800 400 mb convective bands form parallel to the shear with

squall lines and convectively coupled gravity waves in the tropics why do most cloud systems propagate westward abstractthe coupling between tropical convection and zonally propagating gravity waves is assessed through fourier analysis of high resolution 3 hourly 0 5 satellite rainfall data results show the familiar enhancement in power along the dispersion curves of equatorially trapped inertia gravity waves with implied equivalent depths in the range 15 40 m i e pure gravity wave speeds in the range 12 20 m s 1 here such wave signals are seen to extend all the way down to zonal wavelengths of around 500 km and periods of around 8 h suggesting that convection wave coupling may be important even in the context of mesoscale squall lines this idea is supported by an objective wave tracking algorithm which shows that many previously studied squall lines in addition to 2 day waves can be classified as convectively coupled inertia gravity waves with the dispersion properties of shallow water gravity waves most of these disturbances propagate westward at speeds faster than the background flow to under

convection initiation by density currents role of convergence shear and dynamical organization abstract steady state analytic models establish two key points concerning the impact of vertical shear on density currents and the implication for convection initiation first shear decreases the horizontal convergence and therefore the mean ascent associated with downshear propagating currents second shear has a basic effect on the dynamical organization if the downshear current travels at the speed of the ambient flow at a critical steering level an overturning circulation provides deep lifting although mean ascent is increased by shear in the case of upshear propagating currents the lifting is comparatively shallow because jumplike ascent occurs rather than deep overturning the convection initiation mechanism involving the downshear current is therefore very different from the upshear case these basic principles are borne out in two dimensional numerical simulations density currents generated by a stationary cold source imposed on an initially horizontally homogeneous sheared and neutra

determining the δ47 acid fractionation in dolomites abstract this paper reports the fractionation of 47 during the digestion of dolomite in phosphoric acid between 25 c and 90 c using five different samples including three of pliocene age from the bahamas one from the jurassic in the middle east and one obtained from the national institute of standards nist 88b the composition of the dolomites analyzed varied from ca0 56mg0 44co3 to ca0 50mg0 50co3 fractionation values were also compared between the common acid bath and sealed vessel techniques at various temperatures no statistically significant differences were observed either between these two methods or as a function of the dolomite s stoichiometry these data produce a difference in fractionation of 0 153 0 011 for dolomite samples digested at 90 c compared to those reacted at 25 c a value higher and statistically different to previously published values utilization of this value in a study of dolomites from a core drilled on the island of san salvador in the bahamas yielded temperatures and 18ofluid values which agree with previous interpretations on the formation of these dolomites application of this value to other published studies produces lower estimates of temperature and 18ofluid values for the dolomitization process that are more consistent with the geologic models suggested for these studies

evaluation of meteoric calcite cements as a proxy material for mass 47 clumped isotope thermometry abstract meteoric diagenetic cements are ubiquitous throughout geologic history affecting most carbonate exposures worldwide they can often be difficult to interpret as it is usually difficult to separate the influences of water 18o and temperature on isotopic signals contained within the carbonate rock body despite this difficulty in interpretation meteoric phreatic cements can potentially be a useful proxy material as they form slowly in equilibrium at mean annual temperature and are not affected by any biogenic effects that can bias other proxy materials we applied the mass 47 clumped isotope paleothermometer to pleistocene and holocene carbonates from bermuda and barbados in order to investigate the effects of meteoric diagenesis on 47 signals and to determine their suitability as a paleotemperature proxy phreatic calcite cements are found to record the same temperatures as unaltered carbonate sediments while any sample exhibiting vadose characteristics is biased towards unreasonably hot apparent formation temperatures burial heating and re equilibration are not geologically viable explanations for the anomalously hot temperatures recorded in vadose cements as neither bermuda or barbados has any burial history instead it is likely that precipitation in the vadose zone occurs on timescales quicker than isotopic equilibrium can be achieved driven by a combination of co2 degassing and evaporation which have been previously shown to cause problems in speleothems and pedogenic carbonates we conclude by suggesting that meteoric phreatic calcites may be an ideal phase for paleotemperature reconstruction as they accurately record mean annual temperatures and form under equilibrium conditions while also being resistant to further mineral driven diagenesis vadose cements and any sample likely affected by processes similar to vadose diagenesis should be avoided for climate reconstructions using the mass 47 clumped isotope thermometer

isotope hydrology of early paleogene lake flagstaff central utah implications for cordilleran evolution lacustrine sediments from paleogene foreland basins of the north american cordillera serve as powerful integrators of information on climatic and tectonic conditions but episodes of hydrologic connection between basins may confound straightforward interpretations we use stable isotope ratios of carbon and oxygen in authigenic carbonates of the flagstaff formation in central utah to investigate the history of the lake system which produced these sediments flagstaff limestone and dolostone exhibit isotopic compositions consistent with having formed from the same fluid at surface conditions indicating high evaporative concentration was unnecessary to drive dolomite precipitation isotopic data are consistent with the flagstaff formation having been produced by a large lake which occupied its basin from the late paleocene into the early eocene lake flagstaff was hydrologically distinct from lake uinta to the north but may have been connected to lake claron in the south paleoaltimetry estimates suggest that the mean elevation of lake flagstaff9s catchment in the sevier highlands did not exceed 1 5 km the growing evidence from stable isotope data that cordilleran elevations were relatively low in the early paleogene is in stark contrast to structural and sedimentological evidence for a high nevadaplano and a topographically rugged sevier thrust belt

calibration of dolomite clumped isotope thermometry abstract use of the clumped isotope thermometer to decipher environments of dolomite formation has been inhibited by a lack of empirical data from dolomites formed at known temperatures calibrations for aragonite calcite siderite and apatite indicate that a universal 47 temperature relationship may exist across all carbonate bearing mineral phases however theoretical modeling and proposed acid fractionation differences have suggested that dolomites may have different 47 values relative to calcites precipitated at the same temperature to resolve this question we analyzed five synthetic and four natural dolomites formed at known temperatures these included synthetic dolomites grown in mg ca cl solutions at temperatures of 200 250 c and natural samples constrained by fluid inclusion analyses 70 c climate 28 and 27 c and deep ocean borehole temperature 21 c when using calcite 47 acid fractionation values these data result in a calibration line that is statistically indistinguishable from other clumped isotope calibrations at least with current precision we find no evidence for a consistent dolomite 47 offset these results further support a universal calibration for carbonate clumped isotope thermometry and enable new investigations into conditions of dolomite formation

cathodoluminescence in diagenetic calcites the roles of fe and mn as deduced from electron probe and spectrophotometric measurements quantitative spectrophotometric measurements of cathodoluminescence cl intensities of calcite cements from the mississippian lake valley formation are compared with mn and fe electron microprobe analyses of the same calcites cl intensities of these calcites show excellent positive correlation with mn concentrations at approximately constant fe mn ratio and within narrow ranges of fe contents r 0 76 to 0 97 our data suggest that fe mn ratios may control the maximum cl intensity of calcite below this maximum at constant fe mn ratios cl intensity can vary significantly and is controlled mainly by absolute concentrations of mn and fe cl intensities are therefore a function both of absolute concentrations of mn and fe and of fe mn ratios the data further suggest that cl intensities in calcites with low fe concentrations 1 000 ppm are more sensitive to mn activation than to fe quenching cl spectra on the calcites show no evidence of rare earth element activators visual estimates of cl intensities of these calcite cements compare moderately well with intensities measured with the spectrophotometer spectrophotometrically measured cl intensities of calcites in any single visually estimated category bright moderate dull non luminescent overlap with those from adjacent categories thus spectrophotometric measurements are distinctly superior to the visual estimates our data indicate that calcites with more than about 100 ppm mn will luminesce even in the presence of moderate amounts of fe in the absence of detectable fe calcites with about 150 to 650 ppm mn have moderate cl and those with mn contents greater than about 700 ppm have bright cl in the presence of detectable fe the amount of mn required to impart moderate or bright cl increases with fe content furthermore fe does not extinguish mn activated cl up to about 10 000 ppm fe the maximum of our data these results are in general agreement with the electron microprobe study of grover and read 1983 in partial agreement with the data of frank et al 1982 and in poor agreement with the data of fairchild 1983 considering the poor precision of the electron probe at low element concentrations 100 ppm our data are reasonably consistent with the published ion microprobe and atomic absorption data mason 1987 ten have and heijnen 1985 richter and zinkernagel 1981 which imply that mn concentrations in the 30 to 50 ppm range are sufficient to activate cathodoluminescence in calcites

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

the influence of convectively generated thermal forcing on the mesoscale circulation around squall lines abstract the dynamical processes that determine the kinematic and thermodynamic structure of the mesoscale region around 2d squall lines are examined using a series of numerical simulations the features that develop in a realistic reference simulation of a squall line with trailing stratiform precipitation are compared to the features generated by a steady thermal forcing in a dry simulation with no microphysical parameterization the thermal forcing in the dry simulation is a scaled and smoothed time average of the latent heat released and absorbed in and near the leading convective line in the reference simulation the mesoscale circulation in the dry simulation resembles the mesoscale circulation in the reference simulation and around real squall lines it includes an ascending front to rear flow a midlevel rear inflow a mesoscale up and downdraft an upper level rear to front flow ahead of the thermal forcing and an upper level cold anomaly to the rear of the thermal forcing it is also shown t

the paleocene eocene carbon isotope excursion in higher plant organic matter differential fractionation of angiosperms and conifers in the arctic abstract a study of upper paleocene lower eocene p e sediments deposited on the lomonosov ridge in the central arctic ocean reveals relatively high abundances of terrestrial biomarkers these include dehydroabietane and simonellite derived from conifers gymnosperms and a tetra aromatic triterpenoid derived from angiosperms the relative percentage of the angiosperm biomarker of the summed angiosperm conifer biomarkers was increased at the end of the paleocene eocene thermal maximum petm different when observed with pollen counts which showed a relative decrease in angiosperm pollen stable carbon isotopic analysis of these biomarkers shows that the negative carbon isotope excursion cie during the petm amounts to 3 for both conifer biomarkers dehydroabietane and simonellite comparable to the magnitude of the cie inferred from marine carbonates but significantly lower than the 4 5 of the terrestrial c29 n alkane m pagani n pedentchouk m huber a sluijs s schouten h brinkhuis j s sinninghe damste g r dickens and the iodp expedition 302 expedition scientists 2006 arctic s hydrology during global warming at the paleocene eocene thermal maximum nature 442 671 675 which is a compound sourced by both conifers and angiosperms conspicuously the angiosperm sourced aromatic triterpane shows a much larger cie of 6 and suggests that angiosperms increased in their carbon isotopic fractionation during the petm our results thus indicate that the 4 5 c29 n alkane cie reported previously represents the average cie of conifers and angiosperms at this site and suggest that the large and variable cie observed in terrestrial records may be partly explained by the variable contributions of conifers and angiosperms the differential response in isotopic fractionation of angiosperms and conifers points to different physiological responses of these vegetation types to the rise in temperature humidity and greenhouse gases during the petm

assessment of the clumped isotope composition of fossil bone carbonate as a recorder of subsurface temperatures abstract bone is susceptible to early diagenesis and its carbon and oxygen isotopic compositions have been suggested to reflect conditions in the soil environment and shallow subsurface during fossilization this implies open system recrystallization involving mass exchange of carbon and oxygen among bioapatite soil water and dic such recrystallization would also redistribute isotopic clumping including 13 c 18 o bonds leading to the possibility that the carbonate clumped isotope compositions of fossil bone record ground temperature during early diagenesis we assess this possibility by studying quaternary mammalian fossil bone from subtropical to polar latitudes if recrystallization is early and pervasive clumped isotope derived temperatures t 47 should closely mirror latitudinal gradients in ground temperature excluding results from a mummified specimen yielding t 47 38 c that is indistinguishable from mammalian body temperature we find that t 47 values are intermediate between mammalian body temperature and ground temperature suggesting partial recrystallization of bone carbonate xrd analyses show that the nature and extent of diagenesis varies among the samples and does not relate in a straightforward manner to t 47 no clear correlation exists between t 47 and mean annual temperature or mean warm season temperature furthermore bone tends to retain the 18 o enriched signature of body water suggesting incomplete oxygen isotope exchange with meteoric waters incomplete carbon and oxygen isotope exchange between bone carbonate and soil waters is also indicated for a set of late miocene bone enamel pairs from a sequence of stacked paleosols in northern china analysis of bone as old as early cretaceous shows that bone carbonate is susceptible to later diagenesis at elevated burial temperatures although t 47 does not closely conform to maximum burial temperature again suggesting partial recrystallization or recrystallization during different stages of the burial and exhumation circuit these results show that carbon oxygen and clumped isotopes in fossil bone are capable of recording aspects of early diagenesis and the subsequent burial and exhumation history but that distinguishing among different effects is challenging however clumped isotopes in bone can provide useful directional constraints on past temperatures for example t 47 values higher than body temperature necessarily place lower limits on maximum burial temperatures and those lower than body temperature place upper limits on minimum fossilization temperatures

investigation of early eocene water vapor transport and paleoelevation using oxygen isotope data from geographically widespread mammal remains the oxygen isotope composition 18 o of apatite from mammalian tooth enamel can be used to infer the 18 o value of ingested water which is in turn related to that of precipitation stored in surface reservoirs therefore the 18 o value of phosphate from fossil tooth enamel can be used to infer the 18 o value of these reservoirs in the past in this paper tooth enamel from a semiaquatic mammal taxon coryphodon collected from five early eocene localities in north america is used to construct patterns in 18 o values of river water for this time period at all localities the 18 o value of river water 18 o r is estimated to have been higher during the early eocene relative to present day north american rivers although the 18 o vs latitude gradient was shallower during the eocene higher 18 o r values are consistent with warmer eocene air masses being able to hold more water vapor and with an increase in the poleward transport of both moisture and latent heat the regular decrease in 18 o r with latitude indicates that global atmospheric circulation patterns and hydrological transport were not much different from those of the present although the shallower 18 o vs latitude gradient during the eocene may reflect regional differences in precipitation evaporation and river recharge at a more regional scale the 18 o value of river water can provide insight into topographic relief during the early eocene in the case of intermontane basins of wyoming differences in average 18 o r values between basins indicate that laramide mountain relief was on the order of 475 m it is suggested that anomalously low 18 o r values reported previously do not provide unambiguous evidence for permanent snow at higher elevations and may instead reflect brief episodes of cooler winters and or altered atmospheric circulation patterns

in search of finiteness the limits of fine resolution palynology of sphagnum peat high resolution analysis of ombrogenous peats often reveals pollen frequencies that change markedly from one sample to the next indicating limited postdepositional mixing this raises the question whether with sufficiently thin samples seasonal differences in pollen deposition can be observed seasonal resolution in peat would provide a dating technique with an accuracy similar to that of other annually banded archives to study the limits of temporal resolution contiguous 0 5 mm thick slices of slightly humified sphagnum section cuspidata peat were palynologically analysed no seasonal patterns in the pollen stratigraphy could be observed this is ascribed to the mixing of pollen grains as a result of small scaled vertical water movements and to the horizontal mode of shoot layering in the sphagnum species the latter process may also be the cause of a smoothed annual signal because of the absence of seasonal differentiation the palynological distinction of annual peat layers is not feasible

spectral reflectance of carbonate minerals in the visible and near infrared 0 35 2 55 microns calcite aragonite and dolomite

a case study on the far field properties of propagating tropospheric gravity waves abstractmesoscale gravity waves were observed by barometers deployed as part of the usarray transportable array on 29 june 2011 near two mesoscale convective systems in the great plains region of the united states simultaneously airs satellite data indicated stratospheric gravity waves propagating away from the location of active convection peak perturbation pressure values associated with waves propagating outside of regions where there was precipitation reached amplitudes close to 400 pa at the surface here the origins of the waves and their relationship to observed precipitation are investigated with a specialized model study simulations with a 4 km resolution dry numerical model reproduce the propagation characteristics and amplitudes of the observed waves with a high degree of quantitative similarity despite the absence of any boundary layer processes surface topography or moist physics in the model the model is forced with a three dimensional time dependent latent heating cooling field that

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

modeling study of a tropical squall type convective line abstract a multidimensional and time dependent cloud scale model is used to investigate the dynamic and micro physical processes associated with convective and stratiform regions within a tropical squall type convective line the evolution of the total convective and stratiform portions of rainfall is also estimated by using model output a three dimensional version of the model covers a horizontal domain about 96 96 km2 frequently the horizontal extent of an observed stratiform region is over a few hundred kilometers therefore a two dimensional version of the model with a 512 km horizontal length is also used to incorporate a complete stratiform region two dimensional model result recapture many interesting features as observed in particular the fractional portion of stratiform rain as well as its fractional area coverage are in good agreement with observations a significant amount of ice particles melted to rain near the freezing level in the trailing part of the modeled squall system during i

use of clumped isotope thermometry to constrain the crystallization temperature of diagenetic calcite we describe an approach to estimating the crystallization temperatures of diagenetic calcites using clumped isotope thermometry a paleothermometer based on the 13 c 18 o bond enrichment in carbonates application of this thermometer to calcified gastropod shells and calcite cements in an early eocene limestone from the colorado plateau reveals a record of calcite precipitation and replacement at temperatures varying from 14 to 123 c the early eocene host sediments were never deeply buried but they experienced a significant thermal pulse associated with the emplacement of a late miocene basalt flow the combination of independent constraints on thermal history with clumped isotope thermometry petrographic including cathodoluminescence observations and oxygen isotopic data provides an improved basis for estimation of the temperature and timing of diagenetic events and fluid sources the petrography and calcite 18 o values taken alone suggest that the aragonite to calcite transformation of gastropod shell material occurred simultaneously with early formation of cements and lithification of the matrix in the same sample however addition of clumped isotope thermometry demonstrates that this phase transformation of shell material occurred at temperatures of 94 123 c in a highly rock buffered microenvironment i e with the isotopic composition of fluid buffered by coexisting carbonate millions of years after lithification of the matrix and formation of initial low temperature 14 19 c calcite cements within shell body cavities clumped isotope temperatures in excess of reasonable earth surface conditions recorded by later formed cements demand that cement growth occurred in association with the lava emplacement our results illustrate the potential for clumped isotope thermometry to constrain conditions of diagenesis and guide interpretations that would not be possible on the basis of conventional stable isotopic and petrographic data alone and demonstrate how petrographic characterization of clumped isotope thermometry samples can benefit paleoclimate studies

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

mechanisms of petm global change constrained by a new record from central utah catastrophic carbon release and global warming during the paleocene eocene thermal maximum petm profoundly affected continental climate and ecosystems understanding of the details and mechanisms of these effects is limited by the poor geographic coverage of existing continental petm records here we extend the record of this event in north america through identification of the petm carbon isotope excursion within a sequence of paleosols in the north horn formation of central utah some 500 km to the south of previous records from northern wyoming data from the new site suggest that patterns of climatological change were similar across a meridional transect of western north america but that petm climate was relatively more arid in the southern rocky mountains possibly reflecting diversion of precipitation from middle to high latitudes our results are consistent with two proposed mechanisms explaining variation in the amplitude of continental petm carbon isotope records in terms of changes in floral composition or varying environmental wetness and they present opportunities for future tests of proposed north south biotic dispersal during the petm

annual cycle of equatorial east west circulation over the indian and pacific oceans abstract along the equator annual mean 200 mb zonal wind is approximately in phase with annual mean outgoing longwave radiation olr namely easterlies are strongest above the convective center over the maritime continent while westerlies reach their maximum just above the dry zone over the equatorial pacific this is much different from what is anticipated by theories that predict that the phase of the upper tropospheric zonal wind is in quadrature with that of the prescribed heating the present study provides evidence that the midlatitude equatorial coupling is primarily responsible for the maintenance of the annual mean total 200 mb zonal winds along the equator whereas convection contributes a great deal to the annual mean upper level equatorial divergent winds annual cycles occurring over the extratropics act as a transient eddy forcing of the equatorial annual mean 200 mb zonal wind through three dimensional convergence of localized eliassen palm e p fluxes they are acting to accelerate th

equable climates during the early eocene significance of regional paleogeography for north american climate the character of continental interior paleoclimate at mid latitudes especially the aspect of temperature has been a major source of debate in modeling and paleontologic communities over the past few years a recent climate modeling study provides new insight into the issue of climatic conditions of early eocene north america model cases with six times the present level of co 2 or with doubled present co 2 and a large lake in western north america produced results most similar to proxy paleoclimate interpretations it is significant that the north american continental interior climate responded as strongly to the existence of the lake as to the atmospheric co 2 level the large lake deflects the winter freeze line poleward of the region containing most paleoclimate data site locations producing above freezing winter temperatures and providing a possible solution to the minimum temperature difference that exists between models and data the effect of the lake upon regional climate is significant and proves to be critical to reproducing the early eocene climate of north america

the burial and exhumation history of the liuqu conglomerate in the yarlung zangbo suture zone southern tibet insights from clumped isotope thermometry abstract the liuqu conglomerate exposed along the yarlung zangbo suture zone yzsz in southern tibet archives not only the process of the india asia collision but also the exhumation history of the india asia collision zone the burial and exhumation history of the liuqu conglomerate thus could potentially provide clues to the india asia collision and orogeny low temperature thermochronometric data indicate that maximum burial temperatures of the liuqu conglomerate ranged from 80 to 110 c however the exact burial history is not well constrained here we examine the burial conditions of the liuqu conglomerate by applying clumped isotope thermometry to paleosol carbonates extensive microcrystalline recrystallization indicates that the samples have been diagenetically altered during burial moreover the clumped isotope temperatures ranging from 48 to 97 c are clearly above earth surface conditions indicating the original climatic information was overwritten by alteration at higher burial temperatures nevertheless the calculated diagenetic water 18o values represent maximum meteoric water values that can be used to broadly constrain the paleoelevation the highest clumped isotope temperature implies that the maximum burial temperature of the liuqu conglomerate was at least 97 c we conclude that the liuqu conglomerate was buried as deeply as 3 7 4 3 km during the latest paleocene to eocene and then exhumed during the miocene 10 12 ma incision of the paleo yarlung river was likely responsible for erosion and exhumation of the liuqu conglomerate which suggests that the drainage system of paleo yarlung river was similar to that of today and supports the model of outward growth of the tibetan plateau

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

gravity waves in shear and implications for organized convection abstract it is known that gravity waves in the troposphere which are often excited by preexisting convection can favor or suppress the formation of new convection here it is shown that in the presence of wind shear or barotropic wind the gravity waves can create a more favorable environment on one side of preexisting convection than the other side both the nonlinear and linear analytic models developed here show that the greatest difference in favorability between the two sides is created by jet shears and little or no difference in favorability is created by wind profiles with shear at low levels and no shear in the upper troposphere a nonzero barotropic wind or equivalently a propagating heat source is shown to also affect the favorability on each side of the preexisting convection it is shown that these main features are captured by linear theory and advection by the background wind is the main physical mechanism at work these processes should play an important role in the organization of

diurnal patterns of rainfall in northwestern south america part ii model simulations abstract this second paper of a three part series documents the ability of the fifth generation pennsylvania state university ncar mesoscale model mm5 to successfully replicate some known aspects of the rainfall of northwestern south america the success of the control simulation justifies the use of the model in part iii for sensitivity experiments and more detailed diagnosis the simulation is produced using multiply nested grids with grid increments from 72 km down to 2 km three coarser resolution grids are integrated for a period of 10 days with the finest resolution grid run for a 2 day subset of that period several features of the rainfall field are examined as metrics of the model s performance on the largest scales the model reasonably simulates easterly waves in the western atlantic and caribbean although it tends to develop them into tropical cyclones too readily over the amazon river basin diurnally initiated rainbands are observed to propagate westward crossing the basin in 2 3 day

generation and trapping of gravity waves from convection with comparison to parameterization some parameterizations of gravity wave mean flow forcing in global circulation models gcms add realism by describing wave generation by tropospheric convection because the convection in gcms is itself a parameterized process these convectively generated wave parameterizations necessarily use many simplifying assumptions in this work the authors use a realistic simulation of wave generation by convection described in previous work which was validated by observations from the darwin area wave experiment dawex to test these assumptions and to suggest some possible improvements to the parameterizations in particular the authors find that wave trapping in the troposphere significantly modifies the spectrum of vertically propagating waves entering the stratosphere above convective wave sources and offer a linear method for computing wave transmission and reflection effects on the spectrum suitable for inclusion in the parameterizations the wave fluxes originate from both a time varying heating mechanism and an obstacle effect mechanism acting in the simulation methods for including both mechanisms in the parameterizations are described waves emanating from the obstacle effect remain very sensitive to the depth of penetration of latent heating cells into an overlying shear zone which will continue to make it difficult to accurately parameterize in a gcm where the convective cells are not resolved

reworked calcretes their significance in the reconstruction of alluvial sequences permian and triassic minorca balearic islands spain the permian and triassic of minorca balearic islands consists of a 670 m thick red alluvial succession that includes in situ calcrete profiles and reworked calcrete material in the permian succession the calcretes vary from laminar forms developed on the carboniferous basement to weakly developed nodular calcretes in fluvial sediments the palaeosols in the triassic are mostly dolomitic and the profiles reach up to stage iii of soil development spec pap geol surv am 203 1995 1 the clasts formed through reworking of the palaeosol profiles are about 0 5 10 cm across and include mosaics of calcite dolomite crystals brecciated clasts rhizolith fragments and aggregates of clay and or silt these clasts appear in three different types of deposits type 1 corresponds to lenticular bodies that fill small scour surfaces and consists only of intraformational conglomerates these deposits are interpreted as ephemeral channels and sheet floods that represent the interfluvial drainage systems that captured only the precipitation falling on the alluvial plain type 2 includes sand dune 3 d bodies with flat bottoms and convex tops these bodies are about 20 cm high and 2 m wide and were formed by floodwaters that flowed down the levees of the major streams type 3 channel deposits contain reworked calcretes and extrabasinal clasts which overlie erosive surfaces and are found in layers within cross bedded sandstones and conglomerates these are interpreted as channel floor lag deposits of major channels that entered from distant uplands and drained the alluvial plain variations in the aggradation rates of the floodplain resulted in five different infill stages in the lowstand to early transgressive interval as in stages i p1 and iv b1 the fluvial deposits filled palaeovalleys calcretes and reworked calcrete deposits were of difficult formation apart from terraces and preservation accommodation space was at its greatest in the transgressive stages ii p2 and v b2 this caused the greatest aggradation of the floodplains which are formed of thick sequences of fine grained sediments isolated meandering channels weakly developed calcretes compound and reworked calcrete deposits mostly of types 1 and 2 the density of channels notably increased in stage iii p3 highstand interval because of the reduction of accommodation space this could favour the formation of composite or even cumulative palaeosols but of difficult preservation reworked calcrete deposits are mostly of type 3 but types 1 and 2 are also recognised the reworked calcrete deposits are an important part of the permian and triassic fluvial sediments and their occurrence and characteristics are important in order to interpret the infill of terrestrial basins and the construction of floodplains

carbonate stable and clumped isotopic evidence for late eocene moderate to high elevation of the east central tibetan plateau and its geodynamic implications

kinematic and thermodynamic characteristics of the flow over the western pacific warm pool during toga coare abstract rawinsonde and satellite infrared radiation ir data from the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare are used to investigate mean and transient behavior and horizontal variability of the atmosphere over the western pacific warm pool infrared data for the 4 mo intensive observing period iop and vertical motion fields indicate that the intensity of convection height of maximum upward motion and sst all increased from west 140 e to east across the coare domain iop mean ir data show a double itcz intertropical convergence zone structure north and south of the intensive flux array ifa centered at 2 s 156 e although marked variability in the patterns occurred on a month to month basis three prominent westerly wind bursts occurred over the ifa during the 4 mo iop in association with the intraseasonal oscillations isos strong upward motion usually occurred 1 3 weeks prior to the peak low level westerlies subsidence dominated when

climatic and diagenetic signals in the stable isotope geochemistry of dolomitic paleosols spanning the paleocene eocene boundary abstract the precipitation of primary dolomite in soil is rare and controversial and its occurrence indicates highly unusual geochemical and climatic conditions we utilize isotopic and petrographic techniques including clumped isotope thermometry to evaluate diagenetic alteration and preservation of primary climatic signal in dolomitic paleosol nodules from a section spanning the paleocene eocene boundary in central utah isotopic measurements differentiate samples into groups that may be interpreted in terms of alteration however moderate burial depths and extreme warmth during the interval of soil formation make it difficult to reach definitive conclusions from isotope values alone with the addition of petrographic analysis including cathodoluminescence and scanning electron microscopy we are able to identify textural differences between samples suggesting differing amounts of recrystallization we conclude that while some nodules have experienced significant diagenetic alteration the original nodule mineralogy is dolomite and the majority of sampled nodules retain a primary paleoclimate signal early paleogene temperatures recorded at this site are considerably warmer than those suggested for the continental interior from alternate proxies a result that may be partially the result of the clumped isotope temperatures recording warm season soil temperatures rather than mean annual air temperature soil water isotopic composition is suggestive of heightened aridity particularly through the paleocene eocene thermal maximum petm

paleoenvironmental isotope geochemistry and paragenesis of lacustrine and palustrine carbonates flagstaff formation central utah u s a abstract the early paleogene flagstaff formation on the wasatch plateau of central utah preserves a ca 300 meter thick sequence of palustrine and lacustrine limestone and dolostone these rocks formed during a climatically dynamic interval of earth s history and contain important sedimentological and geochemical records of early paleogene greenhouse climate the flagstaff carbonates also document a multiphase history of diagenetic alteration that must be clearly differentiated in order to extract a paleoenvironmental record we have studied the stable carbon and oxygen isotope geochemistry of sample suites from three local stratigraphic sections in conjunction with observations from field studies petrography and x ray diffraction analysis our results provide evidence for a paragenetic sequence including primary carbonate deposition in a shallow freshwater to saline lake system primary or early secondary formation of micritic dolomite episodic exposure and pedogenesis and late stage pressure solution and cementation stable isotope data indicate that the isotopic composition of cements is distinct from but largely determined by that of the host micritic carbonate and suggest that isotopic data from micrites and dolomicrites preserve records of lateral and temporal paleoenvironmental changes in lake flagstaff integration of lithological and isotopic evidence indicates the presence of a persistent lateral paleoenvironmental gradient among our study sites and a secular drying trend represented in all three study sections existing age constraints indicate that the desiccation of lake flagstaff occurred during a multi million year interval of global climate warming that was punctuated by extreme transient 200 kyr warmth during the paleocene eocene thermal maximum petm our analysis suggests that changes in the areal extent and chemistry of lake flagstaff can be attributed largely to climatic changes affecting the lake basin and document a multi million year reduction in precipitation evaporation ratios similar to that previously reported from sites in wyoming to the north although the correlation of the petm within the flagstaff fm remains unclear existing constraints are consistent with this event having corresponded to the maximum lowstand of lake flagstaff perhaps providing evidence for regional climatic drying during this episode of global warmth

westward generation of eastward moving tropical convective bands in toga coare mechanisms responsible for westward generation of eastward moving tropical convective bands in the tropical ocean and global atmosphere coupled ocean atmosphere response experiment toga coare are investigated using a two dimensional numerical cloud model sequential generation of new convective bands to the west of an old eastward moving convective band is successfully simulated in an environment of a convectively active day during toga coare characterized by west winds at low levels and strong easterlies aloft it is concluded that the westward generation of new convective bands is explained by a gravity wave mechanism two westward propagating modes excited below the convective cells moving westward relative to the convective bands appear to play an important role a slow propagating mode 15 ms 21 excited by a shallow convective band is ducted in the troposphere under an unstable layer of small richardson number containing its critical level a fast propagating mode 25 m s21 excited by a deep convective band is ducted in the troposphere under the remaining region of the convective cell containing its critical level these two modes propagate horizontally to the west and promote the growth of shallow convection into long lived convective bands a dry model with thermal forcing representing the convective cell showed that preferential excitation of westward propagating waves below the convective cell is due to westward motion and ascension of the convective cell a comparative simulation without the critical level confirms the proposed gravity wave mechanism

ground truthing chemostratigraphic correlations in fluvial systems changes in elemental chemistry have been used to define stratigraphic correlations between wellbores in petroleum basins few publications however relate defined chemical stratigraphy to physical correlations and none have been found that do so in fluvial systems here chemostratigraphy is applied to permian fluvial sediments within the beaufort group of the karoo basin in south africa and a correlation between three logged sections is defined this correlation is tested against physically determined chronostratigraphic correlations achieved using heli lidar data to provide a high resolution correlation between two sections 7 km 4 4 mi apart and mapping of strata using google earth to produce a correlation between sections 25 5 km 15 8 mi apart the chemostratigraphic characterization that is defined using data from fine grained lithologies resulted in the recognition of eight chemostratigraphic packages with thicknesses between 50 and 250 m 164 and 820 ft over a stratigraphic interval of approximately 900 m 2953 ft two distinctive changes in geochemical composition of the coarser lithologies fluvial channel belts were seen over this interval in the two sections that are 7 km 4 4 mi apart higher resolution subdivision of chemostratigraphic packages was achieved to produce four correlative geochemical units 30 60 m 98 197 ft in thickness that provide a high resolution correlation the chemostratigraphic and chronostratigraphic correlations are in close agreement in both the 7 km 4 4 mi and the 25 5 km 15 8 mi spaced sections the thickness of the study interval and spacing of sections is analogous to published chemostratigraphy studies on subsurface sequences thereby ground truthing the use of chemostratigraphy for correlation in subsurface fluvial systems that are to some degree analogous to the beaufort group sediments of this paper

gregarious tropical convection abstract a beat source with a vertical profile like that of observed tropical mesoscale convective systems mcss is shown to cause through inviscid gravity wave dynamics upward displacement at low levels in a mesoscale region surrounding the heating typical values are 10 30 area contraction at the surface everywhere within 270 km of the heating 6 h after it starts as a result conditions near an existing mcs but beyond the area of mcs outflow become more favorable for the development of additional convection this theory predicts that cloud clusters should be gregarious infrared satellite imagery confirms that almost half of the cold cloudiness observed in a month over the oceanic warm pool region was contributed by just 14 objectively defined multiday supercluters

extreme warming of mid latitude coastal ocean during the paleocene eocene thermal maximum inferences from tex86 and isotope data changes in sea surface temperature sst during the paleocene eocene thermal max imum petm have been estimated primarily from oxygen isotope and mg ca records generated from deep sea cores here we present a record of sea surface temperature change across the paleocene eocene boundary for a nearshore shallow marine section located on the eastern margin of north america the sst record as inferred from tex86 data indicates a minimum of 8 c of warming with peak temperatures in excess of 33 c similar ssts are estimated from planktonic foraminifer oxygen isotope records al though the excursion is slightly larger the slight offset in the oxygen isotope record may reflect on seasonally higher runoff and lower salinity

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

late paleocene early eocene climate changes in southwestern wyoming paleobotanical analysis the warmest global temperatures of the cenozoic era occurred in early eocene time following a warming trend that started in late paleocene time the greater green river basin of southwestern wyoming is one of the best areas in the rocky mountains for paleobotanical investigation of the paleocene eocene climatic transition intensive sampling has resulted in the recovery of an estimated 189 species of plant macrofossils from the tiffanian clarkforkian wasatchian and bridgerian land mammal ages the leaf morphologies and taxonomic affinities of these fossils were used in combination with other indicators to evaluate paleocene eocene climates following cool humid conditions in the tiffanian the clarkforkian was humid and subtropical and several plant families with modern tropical affinities appeared however as in the tiffanian clarkforkian floras had low diversity and were dominated by a single species in the birch family mean annual temperature mat rose from an estimated 12 c in the tiffanian to 19 c in the clarkforkian while mean annual precipitation map for the tiffanian and clarkforkian is estimated to have been 130 150 cm little fossil plant material is preserved from the latest clarkforkian or the earliest wasatchian which is thought to have contained an interval of cooling and drying followed by renewed warming by the middle wasatchian the time of the cenozoic thermal maximum the inferred mat was about 21 c and the map was near 140 cm a second influx of plant families with tropical affinities appeared in the area and diversity increased significantly but most plant families known from the clarkforkian persisted species turnover from the clarkforkian to the wasatchian was greater than 80 a second turnover of more than 80 of species but not families from the wasatchian to the early bridgerian accompanied drying and increased seasonality of precipitation the early bridgerian mat is inferred to have been near 20 c and the map to have been about 80 cm except for the tiffanian and possibly portions of the early wasatchian paleoclimates during the study interval were predominantly frost free although the moderating influence of the green river lake system has been suggested as a possible explanation for mild eocene winters in wyoming this study shows that virtually frostfree climates existed in the area prior to and independent of significant lake development

reconstructing carbonate alteration histories in orogenic sedimentary basins xigaze forearc southern tibet abstract carbonate clumped isotope thermometry t 47 and the oxygen stable isotope record 18 o provide critical constraints on the temperature of carbonate mineral formation and isotopic composition of ancient waters used in reconstructions of past climate tectonics and ecological and environmental change the robust use of these proxies requires that carbonate minerals in the rock record retain primary isotopic compositions through often complex post depositional thermal histories new carbonate clumped isotope thermometry and sedimentology data are paired with existing thermochronology and isotope exchange reaction modeling to provide unique constraints on the alteration history of the carbon and oxygen isotopes in tethyan marine carbonates jialazi fm tso jianding group of the xigaze forearc southern tibet within the framework of the textural and isotopic data the effects of early and late burial alteration on 47 and 18 o values of marine rocks that were buried to 4 km above sea level are modeled the alteration products are considered within two well studied mechanistic frameworks water rock recrystallization and solid state reordering of 13 c 18 o bonds at high temperature the proposed alteration model is as follows 1 shallow early diagenesis with water of similar composition and temperature to formation waters infills primary porespace with microspar 2 high temperature rock buffered water rock exchange and partial solid state reordering at 3 4 km depth and 3 near surface low temperature water rock exchange on the exhumation pathway the 47 heterogeneity within individual samples 0 456 to 0 721 requires significant differential alteration on the retrograde path high to low temperature low water rock ratio in which primary compositions and compositions inherited during early burial diagenesis are overprinted with modern meteoric values a low t 47 value is often assumed to record the primary temperature of the depositional environment however samples yielding low t 47 values in the jialazi fm have undergone extensive high temperature water rock alteration and therefore require a mechanism for increasing 13 c 18 o bond ordering on the retrograde pathway while preserving many primary biogenic structures and micritic textures this study highlights the potential significance of late stage low temperature alteration of carbonates derived from orogenic sedimentary basins for studies of terrestrial paleoenvironments and tectonics this study also provides an example framework for combining observational and analytical data to reconstruct a carbonate alteration history of a buried sedimentary package

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

the origin and significance of pedogenic dolomite from the upper permian of the south urals of russia pedogenic carbonate nodules from six sections spanning the continental permian triassic boundary in the south urals russia were analysed morphological petrographic sem and xrd analyses have demonstrated that many of the latest permian palaeosols are dolomitic this dolomite forms the microcrystalline 5 16 m groundmass of the nodules later diagenetic phases represented by coarser crystalline textures were identified as calcite isotopic analysis of the microcrystalline dolomite has revealed it to be similar in isotopic composition to authigenic dolomite forming today in saline soils in alberta canada these data indicate that the dolomite found in these nodules is pedogenic and formed in equilibrium with the atmosphere upper permian pedogenic dolocretes in the studied sections are most frequent in a palaeosols that formed on palaeo highs and b in the latest permian period changhsingian which may indicate that there was an increase in seasonality and evaporation in the south urals region at this time the presence of only calcitic palaeosols in the earliest triassic may reflect a subsequent dramatic change in the basin conditions possibly relating to the permian triassic mass extinction which stopped the conditions that are necessary for dolomite formation