tropical sea surface temperature reconstruction for the early paleogene using mg ca ratios of planktonic foraminifera 1 to understand the climate dynamics of hypothesized past greenhouse intervals it is essential to constrain tropical sea surface temperatures sst yet existing proxy records give conflicting results here we present the first mg ca based study of pre quaternary sst and investigate early paleogene late paleocene through late middle eocene 58 6 39 8 ma tropical temperatures using planktonic foraminifera belonging to the genus morozovella from ocean drilling program site 865 on allison guyot western central equatorial pacific ocean calcification temperatures similar to or warmer than modern tropical sst are calculated using a range of assumptions regarding diagenesis temperature calibration and seawater mg ca long term warming is observed into the early eocene 54 8 49 0 ma with peak sst between 51 and 48 ma and rapid cooling of 4 c beginning at 48 ma these findings are inconsistent with the 18o based sst previously estimated for this site

green river laminites does the playa lake model really invalidate the stratified lake model proponents of the playa lake model have proposed deposition of most of the green river formation microlaminated carbonates including oil shales in lakes that were not perennially stratified meromictic however there is a variety of evidence favoring a meromictic depositional environment 1 close similarity of much of the lamination to varves in modern meromictic lakes 2 evidence that hydrologic events favoring development of meromixis chemical stratification occurred prior to deposition of major accumulations of oil shale 3 mutually exclusive distribution of fossil nekton especially fish and normal lacustrine benthos including mollusks and 4 analogy with a quaternary playa that became a meromictic lake following increased inflow the playa lake model is untenable for the typical fish bearing kerogen rich microlaminated sediments these laminites were probably deposited in a large ectogenic meromictic lake a chemically stratified lake that formed when increased fresh water inflow drowned a saline playa complex

dramatic local environmental change during the early eocene climatic optimum detected using high resolution chemical analyses of green river formation stromatolites abstract the eocene green river formation represents a system of lakes that covered parts of what is now wyoming colorado and utah and captures the early eocene climatic optimum eeco 52 50 million years ago or ma the warmest period of the cenozoic era and a period associated with very high levels of atmospheric co2 lakes especially closed basin lakes can respond dramatically to environmental change because of their sensitivity to precipitation and evaporation in this study stromatolites from the rife bed of the green river formation are used as fine scale records of terrestrial paleoenvironmental change during a global hothouse climate and to investigate how the environmental dynamics within the lake system affected the growth of stromatolites the stromatolites are composed of branching microdigitate columns laminated on the 10 100 m scale laminae are grouped in cm scale layers that alternate between calcite fan micritic and mixed microstructures the fan layers are depleted in 18o na and mg ca the micrite layers in contrast are comparatively enriched in 18o na and mg ca the 13c and 18o are strongly positively correlated suggesting the stromatolites formed in a closed basin lake consistent with the regional stratigraphy additionally clumped isotope analyses provide the first quantitative values for water temperatures in lake water from the green river formation 35 c for micrite layers and 28 c for fan layers changes in 18o and sodium ion concentration are likely related to periods of evaporation and recharge and thus can be used to estimate lake volume change during stromatolite growth two models one using sodium ion concentrations in a conserved system the other using rayleigh fractionation and mixing equations to explain changes in oxygen isotopes converge upon similar results for lake volume changes revealing multiple episodes of meter scale lake level rise and fall during the accretion of the 30 cm thick stromatolite because of the broad flat bathymetry of the lake such lake volume and depth changes would have been accompanied by shoreline shifts on the order of tens of kilometers while the stromatolites were actively growing challenging the view of a single stromatolite paleoenvironment in the lake therefore the fan microfabric interpreted here as abiogenic in nature formed in cooler waters when the lake was deeper possibly below a thermocline in contrast the micrite microfabric for which there is evidence of biogenicity formed when the lake was shallow and warm the alternation between biogenic and abiogenic microfabrics present in the rife bed stromatolites is hypothesized to result from dramatic changes in lake level influencing the microbiology and chemistry of the waters in which the stromatolites formed indicating that stromatolite growth can occur under disparate conditions and therefore does not necessarily represent a single facies

cyclicity in the green river formation lacustrine eocene of wyoming abstract basinal facies of the green river formation have two main modes lacustrine and playa the lacustrine mode tipton and laney members accumulated mainly varved oil shale here annual cycles are recorded as varves variations in verve thickness demonstrate el nino enso type and sunspot cycles ripepe et al this volume milankovitch scale cycles are not obvious in lithic variations but gamma ray logs record 1 precessional variations with a mean period varve timed of 19 5 ka and 2 a bundling of these in the ca 100 ka eccentricity cycle in the playa mode wilkins peak member the lithic succession oil shale trona dolomitic marlstone records the precessional drying up of a lake and is again bundled in sets of 5 by the 100 ka eccentricity rhythm the tipton member persisted f r 450 ka the wilkins peak member for ca 1 ma

sequence stratigraphy in lacustrine basins a model for part of the green river formation eocene southwest uinta basin utah u s a abstract in the middle green river formation of central nine mile canyon uinta basin utah several lacustrine dominated intervals 10 m thick comprise aggradational carbonate parasequence sets and a progradational clastic parasequence maximum flooding surfaces are best identified within profundal oil shale that caps some of the clastic parasequences these lacustrine transgressive systems tracts therefore exhibit parasequence stacking patterns unlike typical marine sequences two types of sequence boundary are identified type a sequence boundaries display evidence for a basinward shift in facies across a regionally mappable surface that is an angular or rarely parallel unconformity and they typically juxtapose amalgamated braided fluvial channel sandstone late lowstand systems tract onto the profundal oil shale they also bound depositional sequences that show a distinct asymmetry being dominated by transgressive systems tracts 5 80 m thick highstand systems tracts are less than 4 m thick and may be removed completely by erosion on overlying sequence boundaries other surfaces satisfy only some of the standard criteria of sequence boundaries and are termed type b sequence boundaries type a sequence boundaries mark pronounced base level falls following times when the uinta lake had merged with a lake in an adjacent basin to form a much deeper lake such merging permitted the establishment of a new threshold at higher elevation following lake level balancing type b sequence boundaries are interpreted as marking base level falls from a barely merged lake or a lake that had an outflow over a 200 m stratigraphic thickness type a sequence boundaries are more common upsection indicating that with time a pluvial climate became more pronounced or that the adjacent lake was more easily filled type a sequence boundaries also become angular rather than parallel unconformities upsection suggesting increased tilting of the basin margin over time

zonal mean atmospheric dynamics of slowly rotating terrestrial planets abstractthe zonal mean atmospheric flow of an idealized terrestrial planet is investigated using both numerical simulations and zonally symmetric theories focusing largely on the limit of low plan

geomorphic controls on lacustrine isotopic compositions evidence from the laney member green river formation wyoming oxygen isotope values from lacustrine carbonate in the laney member of the green river formation wyoming exhibit a sudden basinwide 6 upsection decrease in 18 o at ca 49 ma 40 ar 39 ar geochronology constrains the duration of the isotopic shift to 200 000 years this change coincides with a sudden change in lake type from balancedfi lled in the lower laclede bed to overfi lled in the upper laclede bed as well as an increase in the proportion of calcitic 80 calcite out of total carbonate by x ray diffraction xrd samples from 32 to 73 the 18 o shift is correlatable through several locations across the greater green river basin and also coincides with a previously observed shift to less radiogenic 87

traveltime tomography of crosshole ground penetrating radar based on an arctangent functional with compactness constraints abstractregularization has been an effective technique to provide unique and stable solutions for crosshole ground penetrating radar gpr traveltime tomography the traditional form of this method in which a low order differential operator was used commonly yields a smooth solution that may not be appropriate when anomalies occur in block patterns such as voids or irregular objects the minimum support ms functional can be used to improve the resolution of blocky structures however in crosshole gpr traveltime tomography the ms functional is unable to resolve residual artifacts whose departure from an a priori model are smaller than the focusing parameter selected from a trade off curve in addition it would result in severe instability and yield a trade off curve with poorly defined corners when the focusing parameter nears the precision of the apparatus we have developed a new stabilizing functional based on the arctangent at function that effectively removes the artificially small values i

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

geomorphology applied to flooding problems of closed basin lakes specifically great salt lake utah abstract closed basin lakes fluctuate in level and area in response to variations in the climate over their drainage basins rises of the level of these lakes present severe flooding hazards to developments on the lake bed effective planning for development of these lake beds requires a knowledge of the lake level fluctuations that should be anticipated and also the effect of wind earthquakes and human activity on flooding the historic record of fluctuations of the closed basin lakes of the great basin of the western united states is too short to adequately define the recurrence intervals of high lake levels geomorphic evidence can supplement the historic record great salt lake is the largest closed basin lake in the great basin and its lake bed has been the most extensively developed in the 1980s the level of great salt lake rose dramatically in response to a period of much above average precipitation the resulting flooding caused extensive damage to developments on the lake bed and posed serious dilemmas to federal state and local governments studies subsequent to the flooding reveal how geomorphic evidence can supplement the historic record and provide sufficient understanding of the lake s flooding hazard to guide development and planning under the climatic conditions that have existed for the past several thousand years the still water level of great salt lake can be expected to rise to near the historic highstand or slightly above about once every one hundred years wind action extends flooding in some locations to elevations 2 m above the still water elevation of the lake if an understanding of flooding hazards guides the planning and engineering of developments on and around the lake losses from future high lake cycles can be significantly reduced

strontium isotope record of paleohydrology and continental weathering eocene green river formation wyoming sr isotope ratios in carbonate rich lacustrine strata provide highly resolved and geo graphically specific records of past changes in weathering and regional drainage patterns the eocene green river formation is perhaps the best documented pre quaternary la custrine unit in the world therefore these strata are ideally suited for studying the be havior of sr the 87 sr 86 sr ratios measured for primary carbonate in lake expansion contraction cycles of the laney member are directly linked to changing lake facies four distinct cycles are preserved in a 6 4 m interval of the arco washakie basin no 1 core each represented by a vertical succession of transgressive stromatolite facies containing dolomicritic intraclasts laminated micrite facies deposited during lake highstands and lake marginal dolomicrite facies which represent subsequent lowstands initial 87 sr 86 sr ratios range from 0 711 99 to 0 713 31 the least radiogenic isotope compositions are as sociated with laminated micrite that records increased regional runoff from phanerozoic marine carbonate and tertiary volcanic rocks during lacustrine highstands the most radiogenic isotope compositions are associated with dolomicrite recording a higher pro portion of runoff from basin bounding precambrian uplifts and the exposed lake plain during lacustrine lowstand the observed 87 sr 86 sr variations may also be due in part to changes in differential weathering of the surrounding landscape where drier climates are associated with decreased differential weathering and therefore higher 87 sr 86 sr in runoff

stromatolites in walker lake nevada great basin usa record climate and lake level changes 35 000 years ago abstract walker lake is a closed basin remnant of the large pleistocene glacial lake lahontan system that has experienced multiple high amplitude 100 200 m changes in water level over the past 40 000 years in response to changes in climate a laminated carbonate stromatolite composed of varying proportions of calcite fans and micrite was collected from a paleoshoreline located at approximately 58 m above present lake level radiocarbon dating revealed that the stromatolite spans approximately 2000 years of growth from 35 227 to 33 727 calibrated years before present ybp a time period during which paleolake level is not well constrained distinct laminae were drilled along the growth axis and the resulting powders were collected for clumped isotope analyses to generate formation temperatures lake water temperatures during stromatolite formation from which 18 o water was calculated results indicate that the stromatolite experienced an initial increase in temperature and water 18 o values followed by a decrease in both during the course of accretion the resulting temperature and isotopic data were input into a rayleigh distillation model for lakewater evaporation in order to estimate the magnitude of lake level and volume fluctuations over the course of accretion modeling results reveal a lake level decrease between 8 1 and 15 6 m followed by an increase of between 4 3 and 8 8 m during the course of stromatolite growth the results of this study indicate that walker lake experienced significant lake volume change over the course of 2000 years perhaps as a response to precipitation changes driven by fluctuations in the polar jet stream and accompanying changes in regional climate and or evaporation induced changes in lake level these results add to a growing body of research indicating that stromatolites and other lacustrine tufas represent a detailed and extensive terrestrial archive that can potentially be used to reconstruct the timing and magnitude of climate change

13c 18o isotope signatures and clumped isotope thermometry in foraminifera and coccoliths accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes most proxies for temperature are not thermodynamically based appear to be subject to biological processes require regional calibrations and or are influenced by fluid composition as a result their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated independent proxies for past temperature could provide an important means of testing and or expanding on existing reconstructions here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths relate those abundances to independently estimated growth temperatures and discuss the possible scope of equilibrium and kinetic isotope effects the proportions of 13c 18o bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonate containing minerals apatite from fish reptile and mammal teeth calcitic brachiopods and molluscs aragonitic coral and mollusks most species that exhibit non equilibrium 18o 16o 18o and 13c 12c 13c ratios are characterized by 13c 18o bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium with possible exceptions among benthic foraminiferal samples from the arctic ocean where temperatures are near freezing observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species

early non marine life evaluating the biogenicity of mesoproterozoic fluvial lacustrine stromatolites abstract the record of life on land or in non marine environments during the precambrian is sparse limiting our ability to understand life outside of marine settings before the advent of animals stromatolites from such environments are known but demonstrating stromatolite biogenicity remains difficult as stromatolite growth can be controlled by a spectrum of biologic chemical and biologically mediated processes stromatolites from the mesoproterozoic 1 09 ga copper harbor conglomerate an alluvial fan fluvial and lacustrine deposit offer an interesting test for the presence and nature of microbial life in shallow mesoproterozoic non marine settings stromatolites from a siltstone facies are interpreted as biogenic as they contain detrital rich laminae likely indicative of trapping and binding by microbes and fenestral fabrics suggestive of desiccation or lift off structures in mats via the presence of gas perhaps o2 from photosynthesis or other gases from mat decay the stromatolites formed as microbial mats grew over a mudflat or sandflat with carbonate filled desiccation cracks on an erosive topography and thus provide evidence for life in a very shallow predominantly desiccated environment stromatolites from a conglomerate facies are microdigitate and record both isopachous laminae with radial fibrous calcite fans and botryoids typically considered abiogenic in origin as well as wavy conical laminations likely indicative of the former presence of microbial mats the conglomerate facies stromatolites are interpreted to have formed in a flooded braidplain setting with restricted circulation this study supports the suggestion that microbial communities were abundant in non marine environments in the midcontinent rift during the mesoproterozoic it also highlights how variable environmental factors can influence stromatolite growth even in similar depositional settings and with a consistent microbial presence

bacterially induced dolomite precipitation in anoxic culture experiments to study the process of microbial mediated dolomite formation growth experiments were carried out with selected bacterial cultures under anoxic environmental conditions simulating those found in lagoa vermelha a hypersaline lagoon in brazil where dolomite precipitation occurs specifically we report the isolation of a particular strain of sulfate reducing bacteria lvform6 from lagoa vermelha sediment which apparently promotes the formation of nonstoichiometric dolomite sulfate reducing bacteria grown in a synthetic liquid medium produced dolomite during 30 days incubation at 30 c the precipitates have morphologies similar to those observed in lagoa vermelha sediment our results demonstrate that sulfate reducing bacteria can influence dolomite precipitation under controlled lowtemperature anoxic conditions and imply that anaerobic microorganisms can play an important role in carbonate sedimentation they may have been particularly significant in earth s earliest history when a more reducing atmosphere existed

temporal variations in lake water temperature paleoenvironmental implications of lake carbonate δ18o and temperature records abstract 18 o and clumped isotope measurements of lacustrine carbonates provide important records of past terrestrial climate and paleoelevation however one of the primary challenges interpreting these data is constraining the relationship between mineral formation temperature and seasonal and mean annual climate we examined surface water temperature records from 88 lakes across the globe to develop transfer functions that relate seasonal water surface temperature to mean annual air temperature these transfer functions provide a means of reconciling proxy measures of water temperature with annual climatic conditions mean annual surface water temperature is related to mean annual air temperature maat 0 0318 t water 2 2 195 t water 12 607 r 2 0 96 independent of lake size with consistently higher mean water temperatures than air n hemisphere spring april june mean lake surface temperatures maat 0 0097 t water 2 1 379 t water 8 227 r 2 0 94 are only slightly warmer than maat for lakes in all climate zones while summer water temperatures jja maat 0 0055 t water 2 1 476 t water 18 915 r 2 0 90 may be 10 20 c warmer than maat for cold climate lakes comparison of carbonate stable isotopic data from sites with different timescales of carbonate formation such as found along latitude or elevation gradients can lead to large over or underestimates of past temperature accurate paleoclimatic interpretation of isotopic proxies or use of temperature proxy constraints i e fossil leaves to estimate lake temperature and calculate water 18 o thus requires appropriate application of water temperature air temperature transfer functions particularly when considering ancient cool high elevation lake systems

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

length of day and obliquity of the ecliptic 850 ma ago preliminary results of a stromatolite growth model a sinusoidal growth pattern in a columnar stromatolite from the approximately 850 million year old bitter springs formation suggests a method for deducing length of day and other geophysical parameters phototropic microorganisms following the seasonal inclination of the sun are proposed as responsible for the estimated 410 or more laminae daily per sine wave annual a preliminary paleomagnetic analysis yields results consistent with the proposed model

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

basin scale cyclostratigraphy of the green river formation wyoming the fl uviolacustrine wilkins peak member of the eocene green river formation preserves repetitive sedimentary facies that have been interpreted as an orbitally induced climate signal however previous quantitative studies of cyclicity in this member have used oil yield data derived from single locations here macrostratigraphy is used to quantitatively describe the spatiotemporal patterns of three different lithofacies associations from 8 to 12 localities that span much of the basin macrostratigraphic time series demonstrate that there is a reciprocal basinscale relationship between carbonate rich lacustrine facies and siliciclastic rich alluvial facies spectral analyses identify statistically signifi cant periods 90 confi dence level in basin scale sedimentation that are consistent with milankovitch predicted orbital periodicities with a particularly strong 100 k y cycle expressed in all lithofacies associations numerous non milankovitch periods are also recognized indicating complex depositional responses to orbital forcing autocyclic controls on sedimentation or harmonic artifacts although fl uctuations in lake gosiute water level did affect basin scale patterns of sedimentation they are not directly related to the 100 k y short eccentricity cycle as previously supposed instead 100 k y cycles are principally recorded by the recurrence of alluvial environments which exerted a dominant control on basin scale patterns of sedimentation generally thus the hydrologic controls on lake level that have been classically linked to short eccentricity actually occurred at finer temporal scales 100 k y understanding the complex links between orbital forcing and sedimentation in the wilkins peak member is facilitated by analysis of time series that refl ect spatial as well as temporal variability in stratigraphic data macrostratigraphy is therefore promising as an analytical tool for basin scale cyclostratigraphy

stromatolite lamination frequency walker lake nevada implications for stromatolites as biosignatures lamination in stromatolites considered some of the oldest fossils on earth is commonly interpreted to record the periodic response of a microbial community to daily seasonal or perhaps yearly environmental forcing but the inability to date ancient stromatolites precludes an understanding of the lamination formation processes we use high resolution 14c dating of holocene stromatolites from walker lake nevada united states to construct a record of lamination rate over the course of accretion laminae formed with a period of 5 6 1 6 yr lamination at the base of the structure 1 6 2 8 1 9 yr lamination in the middle and 4 5 0 8 yr lamination at the top of the laminated portion the predominant 4 6 yr periodicity indicates that lamination formation is likely more closely related to regional climate forcing e g el nino southern oscillation versus the typical diurnal or seasonal changes in microbial mats traditionally assumed for most ancient stromatolites thus generalizations regarding the influence of microbial mats on stromatolite lamination and the use of stromatolites as biosignatures need careful consideration

carbonate clumped isotope thermometry of deep sea corals and implications for vital effects here we calibrate the carbonate clumped isotope thermometer in modern deep sea corals we examined 11 specimens of three species of deep sea corals and one species of a surface coral spanning a total range in growth temperature of 2 25 c external standard errors for individual measurements ranged from 0 005 to 0 011 average 0 0074 which corresponds to 1 2 c external standard errors for replicate measurements of 47 in corals ranged from 0 002 to 0 014 average 0 0072 which corresponds to 0 4 2 8 c we find that skeletal carbonate from deep sea corals shows the same relationship of 47 the measure of 13 c 18 o ordering to temperature as does inorganic calcite in contrast the 13 c and 18 o values of these carbonates measured simultaneously with 47 for every sample differ markedly from equilibrium with seawater i e these samples exhibit pronounced vital effects in their bulk isotopic compositions we explore several reasons why the clumped isotope compositions of deep sea coral skeletons exhibit no evidence of a vital effect despite having large conventional isotopic vital effects

linking the wasatchian bridgerian boundary to the cenozoic global climate optimum new magnetostratigraphic and isotopic results from south pass wyoming new paleomagnetic and stable isotopic results from the northeastern margin of the greater green river basin south pass wyoming provide a refined geochronological context for the wasatchian bridgerian land mammal age boundary and suggest the existence of large amplitude milankovich scale carbon and oxygen isotopic oscillations in this area during the early eocene analysis of 55 paleomagnetic sites through a 310 m section of wasatch green river and bridger formations indicates several reversals that can be correlated to the geomagnetic polarity time scale using radiometric age constraints this correlation places the wasatchian bridgerian boundary in chron c23r at about 52 ma approximately two million years older than previous estimates this new correlation suggests that the mammalian turnover which characterizes the wasatchian bridgerian boundary is coincident with the onset of the cenozoic global climate optimum the warmest interval of the entire cenozoic intrabasinal magnetostratigraphic correlation supports earlier claims that community composition and biostratigraphic datums of basinmargin faunas can differ significantly from coeval basin center faunas oxygen and carbon isotopic composition of paleosol carbonates show in phase cyclic variations on the order of 6 and 3 5 respectively based on the preferred magnetostratigraphic correlation the four best defined cycles represent 397 thousand years indicating potential forcing by variations in orbital eccentricity oxygen isotopic variations may be tracking wet dry cycles amplified by adjacent changes in levels of paleolake gosuite carbon isotopic variations may be tracking the vegetative response to these climate variations alternative interpretations involve cyclic changes in pedogenesis driving correlated variations in isotopic inheritance from parent paleozoic carbonate material and the possibility that c4 plants existed in marginal habitats earlier in geological time than previously thought q 2001 elsevier science b v all rights reserved

10 k y depositional cyclicity in the early eocene stratigraphic and 40ar 39ar evidence from the lacustrine green river formation ar 39 ar dating of sanidine from two interbedded tuffs reveals that the maximum average duration of depositional cycles in the wilkins peak member green river for mation was 10 k y marking the first time that subprecessional cycles have been rec ognized in lacustrine strata the origin of these cycles is uncertain but may relate to a nonlinear climatic response to orbital forcing of insolation alternatively regional tectonic and geomorphic controls on drainage stability may have promoted autocyclic delivery of sediment to the lake owing to an interaction between basin floor relief and varying am plitudes of lake expansion only one third of the cycles identified near the basin center are present near the basin margin this spatial variability in the temporal completeness of the stratigraphic record is not apparent from examination of individual localities indi cating that studies based on time series analysis from other lacustrine systems may need reevaluation

high resolution stratigraphy of an underfilled lake basin wilkins peak member eocene green river formation wyoming u s a abstract lakes tend to respond noticeably to minor changes in sediment and water balance driven by climatic tectonic or geomorphic processes this unique behavior of lacustrine basins can provide a high resolution record of geologic processes within the continental setting far from the globally averaged record of marine strata the wilkins peak member of the eocene green river formation in wyoming usa is dominated by aggradation of repetitive sedimentary facies successions recording distinct lacustrine expansions and contractions these lacustrine cycles consist of up to four successive facies associations littoral profundal sublittoral palustrine and salt pan because they comprise disparate facies that may never have been simultaneously deposited in the basin wilkins peak member cycles are non waltherian successions that do not readily equate to any established sequence stratigraphic unit the completeness of the stratigraphic record in the wilkins peak member varies continuously across the basin at least 126 cycles are present in the erda white mountain 1 core near the basin depocenter whereas only about one third as many are recognizable 53 km north nearer to the basin margin cycle boundaries terminate northward by gradual amalgamation into palustrine facies reflecting the interplay between varying lake levels and a south dipping deposition gradient evidence for complete desiccation and hiatuses is commonplace even near the basin center a truly complete record may not be present anywhere based on recent 40ar 39ar geochronology of tuffs the average cycle duration in the white mountain 1 core is approximately 10 000 years however the true average duration is shorter due to the presence of lacunae and the time required for deposition of the thinnest cycles may have been less than 1000 years no external driving mechanism is presently known for eocene cycles of such short duration raising the possibility that they are instead autogenic cycles related to geomorphic instability of the surrounding landscape evaporite deposition corresponded closely in time and space to maximum differential subsidence suggesting that tectonic influences on drainage patterns and basin accommodation exerted a primary control differential accommodation was most pronounced during deposition of the lower wilkins peak member and became progressively less so after that time based on structural and stratigraphic observations a period of increased tectonic uplift commenced concurrent with deposition of the lower wilkins peak member

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

stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks stromatolites are attached lithified sedimentary growth structures accretionary away from a point or limited surface of initiation though the accretion process is commonly regarded to result from the sediment trapping or precipitation inducing activities of microbial mats little evidence of this process is preserved in most precambrian stromatolites the successful study and interpretation of stromatolites requires a process based approach oriented toward deconvolving the replacement textures of ancient stromatolites the effects of diagenetic recrystallization first must be accounted for followed by analysis of lamination textures and deduction of possible accretion mechanisms accretion hypotheses can be tested using numerical simulations based on modern stromatolite growth processes application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during archean and older proterozoic times but that younger proterozoic stromatolites grew largely through the accretion of carbonate sediments most likely through the physical process of microbial trapping and binding this trend most likely reflects long term evolution of the earth s environment rather than microbial communities

stratigraphic classification of ancient lakes balancing tectonic and climatic controls lakes and lake deposits present two fundamental paradoxes 1 modern lakes are vastly complicated but the rock records of lakes are relatively simple extensive observations reveal three distinct facies associations of common and widespread occurrence these are referred to here as fluvial lacustrine fluctuating profundal and evaporative facies associations 2 most explanations of modern and ancient lakes attribute their nature to climate but neither modern lake parameters lake size depth and salinity nor the character of ancient lake strata thickness extent lithology correlate with measured or inferred climatic humidity we propose that it is the relative balance of rates of potential accommodation mostly tectonic with sediment water fill mostly a function of climate that controls lake occurrence distribution and character lake basins may be termed overfilled balanced fill or underfilled depending on the balance between these rates we conclude that climate and tectonics exert coequal influence on lake deposits at both mesoscales 1 m to hundreds of meters and macroscales hundreds to thousands of meters

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

depositional subenvironments in an arid closed basin the wilkins peak member of the green river formation eocene wyoming u s a the wilkins peak member of the green river formation is a non marine dolomitic deposit that formed in an arid hydrologically closed basin a transect from the margin to the centre of the wilkins peak basin was examined in outcrop exposures in the south eastern corner of the basin and was supplemented with published core descriptions the rocks were divided into seven facies based upon lithology layering style and sedimentary fabrics 1 af facies quartzose conglomerates and sandstones representing sandy alluvial fans coming from the uinta mountains 2 sf facies quartzose peloidal dolomitic sandstones which represent sheet flood deposits extending basinward from the alluvial fans 3 dm facies irregularly laminated dolomitic mudstones with abundant mudcracks which represent sheet flood deposits on a subaerially exposed mudflat 4 el facies dolomitic mudstones with regular lamination and fewer but larger mudcracks representing sporadically exposed lake margins or shallow ponds 5 pl facies finely laminated oil shales and dolomitic mudstones with rare mudcracks which represent shallow perennial lakes 6 sm facies trona or halite deposits with dolomitic mudstone partings or dolomitic mudstones and sandstones disrupted by evaporites of varied morphology these represent a central salt pan and the surrounding saline mudflat 7 as facies arkosic sandstones siltstones and mudstones which represent braided river and more basinal deltaic plain deposits the five dolomitic facies form poorly defined cycles representing the intersection of sheet floods with a lake which transgressed and regressed in response to climatic variations there are at least forty 3 4 m thick cycles in the wilkins peak and one large scale cycle comprising the whole member which mimics the facies changes of the smaller cycles this is compatible with the transitions of the wilkins peak member to the tipton and laney members as climatic responses and not shifts in drainage the sheet flood sandstones actively aggrading subaerial mudflats and bedded evaporites of the wilkins peak are apparently unique within the green river formation they reflect the unusual provenance and hydrology of the wilkins peak and suggest chemical and sedimentary models established for the other green river members will not be applicable

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

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

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