eocene clocks agree coeval 40ar 39ar u pb and astronomical ages from the green river formation u pb ages of zircon from the firehole and analcite ash beds in the eocene green river formation wyoming united states are indistinguishable from 40 ar 39 ar ages of sanidine after adjusting the latter to the astronomically calibrated age of 28 201 ma for the fish canyon sanidine standard six of nine zircon analyses from the firehole ash yield concordant ages in an overlapping cluster and give a weighted mean 238 u 206 pb age of 51 66 0 20 ma full external 2 uncertainty indistinguishable from the recalibrated 40 ar 39 ar age of 51 40 0 25 ma full external 2 uncertainty which is adjusted to eliminate samples with low radiogenic 40 ar significant 238 u 206 pb age scatter likely reflects some combination of minor inheritance pb loss and possibly magma chamber residence seven of eight analyses of analcite ash zircon yield a weighted mean 238 u 206 pb age of 49 23 0 13 ma full external 2 uncertainty whereas the sanidine 40 ar 39 ar age is 49 24 0 18 ma full external 2 uncertainty calibrating green river formation 40 ar 39 ar ages to the 28 201 ma age for fish canyon sanidine permits the first direct comparison of specific green river formation strata to the astronomical solution for early eocene insolation this comparison supports the hypothesis that periods of fluvial deposition coincided with minima in long and short eccentricity and that periods of lake expansion and evaporite deposition correspond to eccentricity maxima

a study of mantle layering beneath the western pacific the reverberative interval of the seismogram defined as the portion following the surface wave train propagating along the minor arc and ending with the first body wave arrivals from the major arc provides an excellent window in which to observe subcritical reflections from mantle discontinuities on an sh polarized seismogram the intervals between scsn and sscsn wave groups zeroth order reverberations are approximately 15 min long and consist almost entirely of waves reflected one or more times from mantle discontinuities first and higher order reverberations we have developed signal enhancement and waveform inversion schemes to progressively extract information pertaining to mantle layering from the waveforms of zeroth and first order reverberations and have applied them to a data set of long period digital seismograms drawn from a number of tectonic regions in and around the western pacific the results place important constraints on the nature of the transition zone discontinuities measurements of the two way vertical shear wave travel time from the free surface to the 400 km and 650 km discontinuities 400 and 650 respectively yield estimates of transition zone travel time tz largely uncontaminated by outside heterogeneity variations in the path averaged estimates of tz are of the order of 5 4 s indicating significant lateral heterogeneity in the transition zone correlations of tz with 400 and lm travel time through the lower mantle are consistent with but do not require the thermal deflection of an exothermic phase transition near 400 km and an endothermic transition at 650 km with 12 km of long wavelength 500 5000 km topography on each the amount of topography estimated for the 650 km discontinuity is significantly less than predicted for a rigorously stratified mantle 100 km in a search for other mantle discontinuities we find evidence for a strong reflector possibly associated with the onset of partial melting in the upper mantle average depth of 86 km due to ambiguity inherent to the method this feature can also be interpreted as an impedance increase in the d region of the lower mantle 70 170 km above the core mantle boundary no evidence is found for a 220 km discontinuity or the d discontinuity proposed by lay and helmberger 1983 suggesting that if such features are present in the western pacific they are either small normal incidence sh reflection coefficient r 1 5 or intermittent or have lateral depth variations well in excess of 50 km

shredding of environmental signals by sediment transport 1 landscapes respond to climate tectonic motions and sea level but this response is mediated by sediment transport understanding transmission of environmental signals is crucial for predicting landscape response to climate change and interpreting paleo climate and tectonics from stratigraphy here we propose that sediment transport can act as a nonlinear filter that completely destroys shreds environmental signals this results from ubiquitous thresholds in sediment transport systems e g landsliding bed load transport and river avulsion this morphodynamic turbulence is analogous to turbulence in fluid flows where energy injected at one frequency is smeared across a range of scales we show with a numerical model that external signals are shredded when their time and amplitude scales fall within the ranges of morphodynamic turbulence as signal frequency increases signal preservation becomes the exception rather than the rule suggesting a critical re examination of purported sedimentary signals of external forcing citation jerolmack d j and c paola 2010 shredding of environmental signals by sediment transport geophys res lett 37 l19401 doi 10 1029 2010gl044638

depositional environments in an arid closed basin and their implications for oil and gas exploration the lower permian fengcheng formation in the junggar basin china the fengcheng formation is a nonmarine carbonate dominated succession that formed under arid climatic conditions in a hydrologically closed basin two transects and two seismic profiles were examined the characteristics and environmental significance of different lithofacies were studied and a model of depositional environment divisions was proposed the sedimentary model involved an alkaline lake in which the depositional environments consisted of a shallow saline lake margin slope saline lake center and steep lake margin from northeast to southwest the perennial central salty lake was located in the southwestern part of the study area whereas there were widespread low gradient lake margins in the northeast east southeast and southern parts of the study area lake level fluctuations had a major influence on the shallow saline lake system and complicated the depositional environments in these areas the deposits are derived from bedrock reworking volcanic eruptions and authigenic minerals that precipitated from brine during the hypersaline phase fine grained terrigenous clastic sediments volcanic ashes and dusts and authigenic minerals mixed in the depocenter concentration center of the brine pool which was covered by high salinity brines and the depositional environment was anoxic as a result of salinity based brine stratification a thick sodium carbonate succession occurred in the depocenter of the ancient mahu lake where bedded sodium carbonate alternated with fine grained organic rich tuff or tuffaceous hydrocarbon source rocks microorganisms bloomed in the alkaline high salinity brine and the organic matter was well preserved which is similar to those modern alkaline saline lakes in eastern africa and western north america thus the permian fengcheng formation contains source rocks that formed in an alkaline saline lake

geochronology and calibration of global milankovitch cyclicity at the cenomanian turonian boundary new 40 ar 39 ar geochronology and global cyclostratigraphic calibration provide high resolution insights into the timing of geochemical fluctuations across oceanic anoxic event ii oae ii five new 40 ar 39 ar data from a single section in western canada suggest an age of 96 4 1 ma for the cenomanian turonian c t boundary this is 3 m y older than previously dated time series analysis e g wavelet transform reveals that oae ii was synchronously deposited worldwide over a period of 320 k y the preservation and stationarity of milankovitch cyclicity in sections across the atlantic indicates that no major fluctuations in sedimentation rate occur across the oae ii except for a minor short term decrease in the rate just before the c t boundary a 13 c org increase of 2 took place at the beginning of oae ii over a period of 110 k y and likely represents a period of worldwide excessive organic carbon burial during transgression leading to a 12 c depletion of seawater and sedimentation this interval was followed by a three step decrease to pre oae ii 13 c values

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

a marine origin for the late mesoproterozoic copper harbor and nonesuch formations of the midcontinent rift of laurentia abstract the c 1 1 ga copper harbor and nonesuch formations of the keweenawan supergroup exposed along the canadian united states shorelines of lake superior are part of the surface exposures of the laurentian midcontinent rift these units have long been considered non marine in origin and have figured prominently in ideas regarding the evolution of microbial life and the redox conditions of earth s ocean atmosphere system at the close of mesoproterozoic time however these rocks also host hydrothermal metal deposits the emplacement of which may have compromised primary geochemical signals that are used to underpin those ideas here we highlight new sedimentological observations to provide an independent framework for assessing the depositional setting and geochemistry of those strata we show that the totality of sedimentological features leads to the conclusion that parts of the upper copper harbor formation and the entirety of the nonesuch formation were deposited along tide and wave influenced shorelines and in shallow marine settings under evaporitic conditions evidence for this interpretation includes the abundance of flaser wavy linsen and pinstripe bedding ubiquity of reactivation surfaces and mud drapes associated with all ripple forms superposed sets of ripple cross lamination showing bimodal herring bone sediment transport directions desiccation cracks and metre scale hummocky cross stratification further evaporite fabrics and pseudomorphs after gypsum in the upper 200 m of the copper harbor formation and in numerous stratigraphic positions within the nonesuch formation indicate that the water body was saline not fresh the emerging palaeogeographic image is one of a large shallow marine embayment with fringing sabkha like shorelines ideas about late mesoproterozoic biospheric evolution and earth s surface redox and oxygenation that rely on the nonesuch formation and copper harbor stromatolites having been deposited within a lacustrine setting require reassessment

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

40ar 39ar geochronology of the eocene green river formation wyoming the deposits of eocene lake gosiute that constitute the green river formation of wyoming contain numerous tuff beds that represent isochronous correlatable stratigraphic markers tuff beds selected for 40ar 39ar analysis occur within laminated mudstone are matrix supported and lack evidence of reworking these tuffs contain 2 15 euhedral phenocrysts of quartz plagioclase sanidine biotite and minor amphibole pyroxene and zircon encased in a matrix of altered glassy ash air abrasion and handpicking under refractive index oils were required to obtain clean unaltered phenocrysts of sanidine 40ar 39ar age determinations from single crystal and 1 mg multigrain aliquots of sanidine and biotite allowed the identification and exclusion of xenocrystic contamination laser fusion experiments on phenocrysts from the rife firehole c bed grey main sixth and analcite tuff beds from the tipton wilkins peak and laney members yielded weighted mean ages 2 analytical uncertainties of 51 25 0 31 ma 50 70 0 14 ma 50 56 0 26 ma 50 39 0 13 ma 49 96 0 08 ma 49 70 0 10 ma and 48 94 0 12 ma respectively ages for sanidine and biotite from the main tuff are indistinguishable when presumably xenocrystic contaminants are excluded from the age calculation moreover the 40ar 39ar ages are consistent with the stratigraphic order of the tuff beds and with provenance in the absaroka and challis volcanic fields our 40ar 39ar based age model indicates that sediment accumulated three times more rapidly 327 86 m yr during the evaporative wilkins peak phase than the freshwater to saline tipton 88 34 m yr and laney 104 18 m yr phases the much lower accumulation rates for the tipton and laney members are permissive of an annual origin for 1 mm thick laminae and precessional forcing of 1 3 m thick depositional cycles in these units however previously described cycles in the wilkins peak member have average durations that are significantly shorter than the 19 23 k y precessional modes the green river formation encompasses an 5 m y period between ca 53 5 and 48 5 ma spanning magnetic chrons 24n through 21r the green river formation was therefore deposited during the warmest period of the cenozoic corresponding to the early eocene climatic optimum as defined by the global marine o isotope record deposition of bedded evaporites trona of the wilkins peak member began at ca 51 ma or 2 m y after the onset of the highest inferred temperatures of the climatic optimum the bridgerian wasatchian faunal turnover occurred subsequently during wilkins peak time at ca 50 6 ma thus our 40ar 39ar ages strongly suggest that wilkins peak evaporite deposition and the turnover from wasatchian to bridgerian fauna were not directly caused by the initiation of maximum greenhouse conditions

cyclostratigraphy and the problem of astrochronologic testing abstract when milankovitch cycles are preserved in the geologic record they provide a direct link between chronometer and climate change and thus a remarkable opportunity to constrain the evolution of the surficial earth system the identification of such cycles has allowed exploration of the geologic record with unprecedented temporal resolution and has spurred the development of a rich theoretical framework for climatic change accompanying these successes however has been a persistent skepticism how does one reliably test for astronomical forcing pacing in stratigraphic and paleoclimate data especially when time is poorly constrained from this perspective it would seem that the merits and promise of astrochronology a phanerozoic time scale measured in 20 000 to 400 000 year increments also serves as its achilles heel if the confirmation of such geologically short temporal rhythms defies rigorous hypothesis testing the implications are substantial since much of our understanding of paleoclimate change throughout the cenozoic and beyond is firmly rooted in astrochronologic interpretation in this study a conceptual framework for assessing earth system response to astronomical insolation changes and the propagation of that signal into the geologic record is used as a guide to understand the nature of the problem of astrochronologic testing this framework emphasizes three challenges contamination stratigraphic distortion and temporal calibration a statistical optimization method timeopt meyers 2015 is formulated as a solution to these three challenges providing an approach for astrochronologic testing that objectively evaluates time scale uncertainty while simultaneously identifying an optimal model for climate and depositional system response to astronomical forcing new extensions to the technique are presented allowing explicit reconstruction of distortions to the primary forcing that are known to be omnipresent in the stratigraphic record to illustrate the utility of this approach it is applied to five well studied stratigraphic series throughout the phanerozoic supporting their astronomical origin and yielding constraints on the evolution of the earth system and the astronomical solutions themselves future directions that build on this foundation are discussed including the utility of process based null models approaches for earth system transfer function reconstruction and mapping out ancient solar system behavior and earth moon history using the geologic archive of milankovitch cycles the timeopt approach recognizes astronomy geochronology paleoclimatology and depositional system reconstruction as a unified geoscientific inverse problem

atmospheric carbon dioxide and early eocene climate a general circulation modeling sensitivity study abstract the early eocene was the warmest time interval of the past 65 million years we have investigated the hypothesis that the warm climate of the early eocene may have been caused by higher than present levels of atmospheric carbon dioxide co2 we have used an atmospheric general circulation model the ncar genesis model coupled to a land surface model and a mixed layer ocean to examine the sensitivity of early eocene climate to varying levels of atmospheric co2 model cases contained a description of the early eocene earth and included either 300 560 or 1680 ppm atmospheric co2 climate responses to increased atmospheric co2 include 1 increased mean annual global temperature by 2 6 c and decreased latitudinal surface temperature gradients 2 maximum warming at high latitudes especially in the winter season 3 increased mean global precipitation 4 increased high latitude clouds in comparison with geological paleoclimate data the climate response to increased co2 does not appear to explain completely the early eocene latitudinal surface temperature gradient for example with the 1680 ppm co2 case high latitude oceans and continents are minimally warm enough to match paleoclimate data while low latitude regions are overly warm when compared to sea surface temperature reconstructions we conclude that co2 was very likely at least double the present level during the early eocene and contributed to the overall character of early eocene climate however consideration of increased poleward oceanic heat transport and or other factors may be required to produce model results that more closely agree with marine and terrestrial paleoclimate data especially at low latitudes

quantification of deep time orbital forcing by average spectral misfit quantification of milankovitch orbital cyclicity within ancient strata has become a principal tool for refinement of the geologic time scale however accurate characterization of the orbital signal in deep time paleoclimate records is commonly challenged by inadequate radiometric time constraints for calibration of the spatial rhythms to temporal periods this problem can potentially introduce large errors into derivative orbital timescales in this study we develop a new method for the identification and calibration of orbital cyclicity in cyclostratigraphic records the method average spectral misfit or asm yields an objective estimate of the optimal sedimentation rate for a stratigraphic interval that preserves a record of orbital forcing the technique also provides a formal statistical test for rejecting the null hypothesis no orbital signal application of the method to assess orbital cyclicity in the upper bridge creek limestone member turonian of the western interior basin highlights the utility of this new cyclostratigraphic tool and provides a means to independently evaluate conflicting interpretations of the lithologic cycles importantly asm offers a new consistent standard by which orbital timescales may be compared hence the quality of an orbital timescale can be formally qualified by reporting its average spectral misfit and null hypothesis significance level this technique will permit improvement of mesozoic cenozoic orbital timescales and extension of orbital time scale development into the paleozoic as the method is not dependent upon well constrained radiometric age data

tracking drainage basin evolution continental tectonics and climate change implications from osmium isotopes of lacustrine systems abstract organic matter in the lacustrine eocene green river formation in two cores separated by 16 km in the uinta basin record similar centimeter scale initial 187os 188os denoted as osi stratigraphic profiles this demonstrates that the os isotopic composition of lacustrine organic matter is spatially homogeneous and in this case documents variation on the time scale of thousands of years the osi stratigraphy developed here indicates temporal change in the os isotopic composition of lake water which is regulated by the os isotopic composition of inflowing chemical weathering products from the surrounding drainage basin although observed osi variability is just above the level of analytical uncertainty it can be modeled with less than a 6 change in water input from radiogenic to nonradiogenic sources this highlights the sensitivity of this isotopic tracer changes in os isotope composition may reflect changes in relative discharge of rivers with different os isotope composition changes in the footprint of the drainage area to include or exclude different rock types or unroofing thus this study suggests that os isotope stratigraphy in lacustrine settings can be used to link basin stratigraphy to changes in the drainage basin which are driven by climatic tectonic and geomorphic processes the similarity in os isotope stratigraphy between the two cores documented here highlights its utility for detailed chronostratigraphic correlation within and between lacustrine basins a conservative sedimentation rate suggests that osi in these lacustrine deposits changed at a rate of 0 01 per kiloyear two orders of magnitude faster than has been reported in marine organic rich sedimentary rocks ravizza 2007 furthermore linear regression of 187re 188os and 187os 188os ratios of all samples yields a model 3 depositional age determination of 48 3 2 8 ma 2 mswd 8 2 which statistically indistinguishable from a weighted mean laser fusion 40ar 39ar sanidine age of 49 58 0 32 ma smith and carroll 2015 of a temporally adjacent volcanic ash

sedimentary record of seismic events in the eocene green river formation and its implications for regional tectonics on lake evolution bridger basin wyoming abstract outcrops and cores from the top of the lacustrine tipton member and the base of the wilkins peak member 51 5 ma of the eocene green river formation bridger basin in southwestern wyoming yield a wide variety of sedimentary deformation features many of which are laterally extensive for more than 50 km they include various types of folds load structures pinch and swell structures microfaults breccias and sedimentary dikes in most cases deformation is represented by hybrid brittle ductile structures exhibiting lateral variation in deformation style these occur in low energy profundal organic rich carbonate mudstones oil shales trona beds tuffs and profundal to sublittoral silty carbonate deposited in paleolake gosiute the deformation is not specific to the depositional environment because sedimentary units stratigraphically higher with similar facies show no deformation the studied interval lacks any evidence for possible trigger mechanisms intrinsic to the depositional environment such as strong wave action rapid sediment loading evaporite dissolution and collapse or desiccation so endogenic causes are ruled out thus the deformation features are interpreted as seismites and change in deformation style and inferred increase in intensity towards the south suggest that the earthquakes were sourced from the nearby uinta fault system the 22 levels exhibiting seismites recognized in cores indicate earthquakes with minimum magnitudes between 6 and 7 minimum epicentral intensity mcs of 9 and varying recurrence intervals in the seismic history of the uinta fault system with a mean apparent recurrence period of 8 1 k y using average sedimentation rates and dated tuffs in detail however there are two noticeably active periods followed by relative quiescence the stratigraphic position of these deformed intervals also marks the transition between two distinct stages in lake evolution from the balanced filled tipton member to the overlying underfilled wilkins peak member thus these seismites are evidence for regional scale changes in lacustrine sedimentation of eocene lake gosiute in response to syndepositional tectonic activity analysis of synsedimentary deformation features is therefore a promising yet under utilized tool to trace the tectonic evolution of lacustrine deposits of the green river formation and other tectonically active marine and non marine basins

macrostrat a platform for geological data integration and deep time earth crust research characterizing the lithology age and physical chemical properties of rocks and sediments in the earths upper crust is necessary to fully assess energy water and mineral resources and to address many fundamental questions in the earth sciences although a large number of geological maps regional geological syntheses and sample based measurements have been produced there is no openly available database that integrates rock record derived data while facilitating large scale quantitative characterization of the volume age and material properties of the upper crust here we describe macrostrat a relational geospatial database and supporting cyberinfrastructure that is designed to enable quantitative spatial and geochronological analyses of the entire assemblage of surface and subsurface sedimentary igneous and metamorphic rocks macrostrat now contains general comprehensive summaries of the age and properties of 33 903 lithologically and chronologically defined geological units distributed across 1 474 regions in north and south america the caribbean new zealand and the deep sea sample derived data including fossil occurrences in the paleobiology database more than 180 000 geochemical and outcrop derived measurements and more than 2 1 million bedrock geologic map units from over 170 map sources are linked to specific macrostrat units and or lithologies macrostrat has generated numerous quantitative results and its data infrastructure is being used in several independently developed mobile applications however it is necessary to expand geographic coverage and to refine age models and material properties to arrive at a more precise characterization of the upper crust globally

fe ii oxidation processes at the surface of bacterially colonized iron deposits abstract fe ii oxidation processes at the surfaces of bacterially colonized iron deposits are examined at three hot springs in japan for which the chemical profiles of the ph redox and o2 and fe ii concentrations at the water deposit interface are measured via microelectrodes the three hot springs share similar bulk chemistry with a weakly acidic ph of 5 7 6 3 a high iron concentration of 50 130 m and a high dissolved inorganic carbon concentration of 20 60 mm at the sambe and shionoha hot springs where the bulk water o2 concentration is ca 80 m abiotic fe ii oxidation via autocatalysis prevails at the okuoku hachikurou hot spring where the bulk water o2 concentration is ca 50 m autocatalytic fe ii oxidation is suppressed and biotic fe ii oxidation induced by cyanobacterial photosynthesis is effective these observations indicate that an o2 concentration of ca 50 m is the threshold of reversing the relative contribution of biotic and abiotic fe ii oxidation protons from fe ii oxidation are compensated by reactions among the dissolved inorganic carbon species which sustain the ph condition and continuous fe ii oxidation at the deposit surface the observations of this study provide implications for understanding the deposition of banded iron formations in the geological past

on the relationship between macrostratigraphy and geological processes quantitative information capture and sampling robustness abstract spatial and temporal patterns in the sedimentary record are controlled by a wide range of forcing mechanisms macrostratigraphy uses the temporal ranges of gap bound rock packages compiled separately for different geographic locations to quantify these patterns the total number of gap bound packages d and the rates of package initiation and truncation p and q respectively distill depositional geometries into time series that preserve information on both the spatial extent and the temporal continuity of deposition these macrostratigraphic quantities should in principle relate quantitatively to the underlying forcing mechanisms that govern sedimentation here we use a numerical model of continental margin sedimentation to test the extent to which time varying forcing mechanisms including subsidence sediment supply and sea level change can be detected quantitatively by the application of macrostratigraphy spectral and information theoretic analyses of time series of d p and q show

spectral effects of time depth nonlinearities in deep sea sediment records a demodulation technique for realigning time and depth scales carbon 14 dating and percent caco3 in late pleistocene sediments suggest that deepsea sedimentation rates vary cyclically and that this cyclicity is related to climate sedimentation rate variability leads to nonlinearity in the time depth mapping function this nonlinearity can have profound affects on signal spectra leading to the development of harmonics and intermodulation tones these distortion effects in the spectra give a direct indication of the degree of nonlinearity thereby providing a tool for realigning time and depth scales a tuning technique is developed which assumes a direct link between climate as measured in 18o from planktonic foraminifer tests and sedimentation rates a criterion of spectral simplicity as quantified in the varimax norm is used to demodulate the input spectrum application of this technique to an equatorial pacific piston core erdc 84 found peak glacial sedimentation rates to be 30 higher than peak interglacial rates a figure in good agreement with 14c based estimates from the same area this technique is compatible with other time scale tuning techniques such as those using orbital parameters and in combination with these other techniques provides a method for fine tuning any late pleistocene record

resolving milankovitchian controversies the triassic latemar limestone and the eocene green river formation although orbital forcing is commonly proposed as the driver of ancient sedimentary rhythms the lack of adequate independent time control radio isotopic data to calibrate these cycles has stood as a major challenge to evaluation of the hypothesis here i apply a new statistical approach to evaluate cyclicity in two historically important rhythmic units for which orbital forcing has been proposed the triassic latemar limestone dolomites italy and the eocene green river formation wyoming usa a major advance of the new method is its explicit evaluation of the null hypothesis of no orbital signal the null hypothesis can be rejected with a high degree of confi dence in the latemar limestone probability 0 30 and green river formation probability 0 07 the analyses also resolve controversies about the specifi c orbital calibrations at each site both data series reveal the expected precession obliquity and eccentricity orbital components and yield astrochronologies that are consistent with proposed radio isotopic based time scales

phase lagged amplitude modulation of hemipelagic cycles a potential tool for recognition and analysis of sea level change many ancient rhythmic hemipelagic sequences have been interpreted to record orbital variations but the exact nature of the climatic and depositional transfer functions responsible for this link remains poorly understood two dimensional numerical simulations were used to explore selected aspects of orbital signal distortion in linked siliciclastic and hemipelagic systems the models suggest that transfer of multiorder e g 20 100 and 400 k y oscillations in relative sea level into the hemipelagic record produces an inherent amplitude distortion of the shorter period e g 20 k y cycle this distortion gives rise to amplitude modulation am which is qualitatively similar to am of orbitally driven changes in insolation e g eccentricity modulation of precession driven cycles however unlike the orbitally driven am synthesized am is distinctly phase shifted relative to the stratigraphic record of the long period e g 100 k y 400 k y cycle as a result of sealevel driven changes in the storage capacity of nearshore through alluvial parts of the source siliciclastic system hence multiorder changes in sea level can leave a distinct am signature in dilution affected hemipelagic records thus making hemipelagic rhythms due to eccentricity forced sea level changes distinguishable from other types of orbitally driven hemipelagic cyclicity

correlation of fluvial strata in the subsurface a review abstract correlation of ancient fluvial strata in the subsurface is challenging due to complex facies architectures and the lateral discontinuity of facies over short distances 10 km the complexity of the strata is due to the interplay of allogenic factors that determine the rate of creation of accommodation sediment supply and ultimately fluvial architectures on regional scales the application of commonly used stratigraphic techniques in such successions has allowed for improved regional correlations and an enhanced understanding of the evolution of basin fills lithostratigraphy biostratigraphy chemostratigraphy magnetostratigraphy event stratigraphy sequence stratigraphy pedostratigraphy chronostratigraphy in particular geochronology cyclostratigraphy and provenance stratigraphy are assessed outlining their benefits drawbacks and application using several case studies lithostratigraphy is highly discouraged as facies boundaries are often time transgressive on the contrary chemostratigraphy event stratigraphy and provenance stratigraphy show excellent potential for correlating ancient fluvial strata as key signatures can be recognized between different localities over distances greater than 25 km the character and thickness of paleosols can also greatly enhance both sequence stratigraphic and pedostratigraphic correlations the most promising correlation technique involves the use of chronostratigraphy in particular geochronology the high precision radiometric dating of tuffs or precisely dating the youngest zircon population in a sandstone sample using u pb ca tims when available provides a precise and independent way to correlate fluvially dominated strata unambiguously over large distances 100 km the integration of several techniques such as sequence stratigraphy in conjunction with pedostratigraphy is also recommended to construct a comprehensive stratigraphic framework for fluvially dominated successions the most appropriate correlation technique is dependent on several factors including budget the purpose and scope of the study and whether the data come from outcrops or the subsurface improved correlations will enhance our understanding of ancient fluvial systems and their resource potential

a strategy for cross calibrating u pb chronology and astrochronology of sedimentary sequences an example from the green river formation wyoming usa abstract astronomical calibration of the geological timescale has been limited until recently by the precision and accuracy of radioisotopic dates especially for pre neogene records uncertainties for radioisotopic dates of older strata were typically much larger than a single precessional cycle and dates were often sparse leading to the practice of orbital tuning of cyclic strata in order to astronomically calibrate the desired interval ideally in order to test the assumptions of astronomical calibration with geochronology it is necessary that the precision of radioisotopic dates be comparable to the period of the cycle being tested the new u pb ca tims chemical abrasion thermal ionization mass spectrometry zircon dates reported here conform to this precision requirement with 2 analytical uncertainties from 11 000 to 52 000 years for seven volcanic ashes from the wilkins peak member of the green river formation the zircon dates have simple distributions with few outliers and allow accurate estimations of the eruption ages with potential inaccuracies of less than precessional cycle the eocene green river formation wyoming usa has long been recognized as a record of cyclicly deposited lacustrine sediments and the abundant intercalated volcanic ashes make it a suitable place to test new approaches to astronomical calibration of cyclic strata the abundance of different types of marker beds including tuffs that are intercalated with the sedimentary cycles guarantee an unambiguous correlation between sampling locations of dated tuffs on the margins of the basin and the basin center where the cyclicity is best developed thus reducing any stratigraphic uncertainties to a fraction of hypothesized precession cycle tuning based orbital age models accepted by the previous geochronology significantly deviate from the new geochronology whereas a previously rejected model that assumes a short eccentricity period of 125 ky is now allowed in order to test possible explanations for the apparent 125 ky period such as changes in orbital periods or gaps in the sedimentary record we present an iterative strategy to select future ashes for dating such that the astronomical calibration testing is optimized we iteratively contrast two ad hoc age models that bracket the linear interpolation between the dated ashes the optimal intervals for further dating are located where the deviations between the models exceed our reported uncertainties we propose that the iterative approach described here should become the standard for establishing a rigorous orbital calibration of the stratigraphic record where sufficient ashes exist

macrostratigraphy of north america abstract the geological record is a three dimensional mosaic of gap bound rock bodies that at any given scale of temporal resolution were emplaced more or less continuously at any geographic location the irregular alternation of processes responsible for the formation and destruction of rock bodies results in the preservation of hiatus bound rock packages that have a distinct time of first occurrence base or oldest portion a time of last occurrence top or youngest portion and a suite of defining characters e g lithologies thickness fossils etc many important aspects of the geologic record can be quantified by compiling the stratigraphic ranges of such gap bound rock packages these include the quantity and spatial and temporal distribution of preserved rock rates of rock formation sequence stratigraphic architecture and area weighted rates of expansion and contraction erosional truncation of rock emplacement settings this approach to characterizing the rock record is scalable per

origin of lacustrine rocks of wilkins peak member wyoming wilkins peak member of the green river formation with its interbeds of trona oil shale and dolomitic mudstone contrasts markedly with the predominantly oil shale and calcitic mudstone sequences of the remainder of the succession much discussion has centered on the origin of these lacustrine rocks a perennial meromictic stratified lake model has been replaced in recent years by a playa lake model the subsurface stratigraphy however was not well known when the models were developed paleogeographic reconstruction indicates that the region was subjected to variations in hydrographic conditions mainly in response to climatic fluctuations during humid subtropical periods widespread during the deposition of the tipton shale member and laney member the lakes were p edominantly open meromictic systems with rivers entering the basin from the north these environmental conditions were modified during deposition of the wilkins peak member as the climate became more arid and along the southern margin of the basin shallow saline alkaline playa lakes formed in response to these changes the widespread occurrence in the subsurface of fluvial clastic sequences of the wasatch formation associated with the wilkins peak member would indicate that the playa lakes were frequently flooded and freshened by southern drainage systems therefore the lakes were continuously undergoing modifications under the influence of climatic and possibly tectonic processes a composite model is supported that combines aspects of both the meromictic and playa lake models beca se of these complexities it is unlikely that one modern lake can serve as an analog for ancient lake gosiute

spectral analysis of the lower eocene wilkins peak member green river formation wyoming support for milankovitch cyclicity abstract this study is the first to employ spectral analysis to examine meter scale sedimentary cyclicity in the wilkins peak member of the lower eocene green river formation of wyoming generally regarded as the classic example for orbital forcing of lacustrine sediments at eccentricity and precession time scales this long standing interpretation was recently contested with a much shorter duration 10 ky inferred for the dominant cyclicity earlier work lacked adequate age control or spectral analysis or both our analysis is based upon an evaluation in the frequency domain of oil yield values from four boreholes accuracy estimation for suggested orbital interpretations and comparison to independent geochronology cored intervals 266 364 m thick represent a span of 1 2 1 7 m y with temporal resolution of 3 5 ky 1 m for oil yield values variations in spectral power with depth within the original records are interpreted to reflect changes in the rate of sediment accumulation these changes are corrected prior to testing the orbital forcing hypothesis by using two methods 1 a minimal adjustment three segments accounting for the dominant changes of spectral frequency with depth and 2 correlating the published definitions of precessional cycles in these records to a 21 ky cosine curve orbital age models resulting from the two tuning methods are compared to available chronology and the tuned records are tested for the expected spectral peaks from orbitally forced records we conclude that the dominant cyclicity of the wilkins peak member is orbitally forced orbital age models overlap 40 ar 39 ar ages and inferred periods include long and short eccentricity weak obliquity and precession eccentricity is resolved in the analyzed records but the expected 95 and 125 ky periods are not resolved controlling the range of possible tuning periods and the accuracy of orbital age models sub milankovitch variability exists and can be resolved to a minimum period of 3 5 ky by the analyzed records however it cannot be characterized fully with the available chronology or by the previously calculated mean cycle duration

limnogeology news in brief we ve invited michael r rosen water quality spe cialist within the usgs water science field team incarson city and elizabeth gierlowski kordesch pro fessor of geology at ohio university to take a look atthe intriguing new developments that are emerging inlimnogeologic studies these studies are increasingour understanding of how climate and movements ofthe earth s surface in uence terrestrial environments as well as how contaminants are distributed andretained in the environment they present a selectionof recent signi cant research on sediments rock andbiota that have been preserved in modern and ancientlake basins limnogeology is a relatively new eld of study in a formalsense in that the term limnogeology was coined in the early1990s although research on how lakes have formed andevolved over time has been studied since at least the 1800s for example russell 1885 gilbert 1890 over the pastseveral years new exciting techniques have been applied tolimnogeologic studies these studies have expanded ourunderstanding of how climate and tectonics affect changein terrestrial environments as these past changes havebeen shown to be important for predicting future climatechange interest in limnogeology has increased in addition understanding how contaminants are distributed and pre served in the environment is essential for protecting wild life and human health lakes form in a diversity of geologic structures and rocktypes as well as all climate zones the diversity of lacus trine geology and biology that contribute to lake sedimentsrequires a multidisciplinary approach to solve importantissues issues such as differences between regional andglobal paleoclimate variations over time tectonic effectsover time changes in contaminant histories with varyingland use within watersheds and the unraveling of hydro logic changes caused by human or natural modi cationswithin a watershed through interdisciplinary techniqueselucidate these problems because of the variety of subjectmatter in lacustrine basins the studies presented here aredivided into studies of contaminants in lake basins ofrecent lake basins unconsolidated lake sediments and ofancient lake basins sediments that have lithi ed into rock contaminants in lake sedimentsone of the most interesting studies of substantial regionalcontamination of lake sediments comes from studies ofpolycyclic aromatic hydrocarbons pahs that are erodedand leached from coal tar based sealants used to protectand enhance the appearance of asphalt pavement primarilyparking lots and driveways in the united states andcanada van metre and mahler 2010 showed that thesealants were a major contributor to pah concentrations insediments of 40 lakes throughout the united states highpah concentrations were noted in central and eastern lakesin the usa where coal tar is more frequently used than inthe west based on ngerprinting of the different pahcompounds in the sediment van metre and mahler 2010

early eocene carbon isotope excursions and landscape destabilization at eccentricity minima green river formation of wyoming repeated global reorganizations of carbon cycling and biotic oceanic and terrestrial processes occurred during the early eocene and appear to have been paced by cyclic variations in the eccentricity of the earth s orbit the phase relationship s between insolation variation terrestrial paleoclimate and atmospheric pco2 during these events remains enigmatic however due to their poorly constrained timing relative to specific orbital configurations here we use tiered interpolation between radioisotopic ages and paleomagnetic polarity chrons to compare high resolution 13c and lithofacies records from the wilkins peak member of the green river formation of western north america to a fe intensity xrf record from the western atlantic ocean and to numerical solutions for earth s orbital configuration wilkins peak member lithofacies stacking patterns record cyclic geomorphic responses to insolation and climate fluctuations spanning an interval of 1 8 ma previous macrostratigraphic analyses using 40ar 39ar and u pb ash bed ages indicate that these cycles reflect long and short eccentricity modulation of precession hydrologic variance appears to have occurred inversely with intervals of maximum sediment advection with carbonate and evaporite dominated lacustrine modes during eccentricity maxima and siliciclastic dominated alluvial modes during eccentricity minima stable carbon isotope analyses of 126 meters of wilkins peak member strata reveal a regular 5 per mil oscillation between high 13c lacustrine modes and low 13c alluvial modes tiered interpolation between paleomagnetically characterized terrestrial ash beds facilitates the integration of 11 radioisotopic ages with the geomagnetic polarity timescale resulting in significant expansion of chron c23 and shortening of chron c22 relative to timescales based on seafloor magnetic anomaly profiles the new proposed timescale permits direct comparison of terrestrial and marine climate proxy records from the early eocene climatic optimum at ca 250 kyr 250 kyr resolution and reveals prominent 100 kyr and 405 kyr scale oscillations within both records wilkins peak member 13c minima which occurred during low eccentricity alluvial modes likely coincided with global 13c minima scenario 1 but may alternatively reflect productivity driven local effects within lake gosiute scenario 2 if scenario 1 proves accurate early eocene negative 13c hyperthermal excursions occurred during eccentricity minima rather than maxima as formerly believed

the evaluation of eccentricity related amplitude modulation and bundling in paleoclimate data an inverse approach for astrochronologic testing and time scale optimization cyclostratigraphic analysis has produced fundamental advancements in our understanding of climate change paleoceanography celestial mechanics geochronology and chronostratigraphy of central importance to this success has been the development of astrochronologic testing methods for the evaluation of astronomical climate influence on sedimentation most pre pleistocene astrochronologic testing methods fall into one of two categories 1 those that test for expected amplitude or frequency modulation imposed by an astronomical signal or 2 those that test for bedding hierarchies frequency ratios or bundling that are predicted by the dominant astronomical periods in this study a statistical methodology for combining these complementary approaches is developed which identifies the time scale that simultaneously optimizes eccentricity amplitude modulation of the precession band and the concentration of power at precession carrier and eccentricity modulator frequencies the technique is demonstrated to have high statistical power it is capable of identifying astronomical cycles when present under a wide range of conditions and its application to synthetic models illuminates a range of potential pitfalls that are encountered when more conventional nonoptimization approaches are used the method is also independent from the interpretation of power spectrum peak significance resolving previous concerns regarding appropriate confidence level assessment and multiple testing as two case studies the algorithm is applied to miocene strata of ocean drilling program odp site 926b and the paleocene eocene thermal maximum eocene thermal maximum 2 interval at odp site 1262 the results verify published cyclostratigraphic interpretations and support the theoretical astronomical solutions this new astrochronologic testing approach can be used to evaluate cyclostratigraphic records spanning the phanerozoic and potentially beyond

highly seasonal and perennial fluvial facies implications for climatic control on the douglas creek and parachute creek members green river formation southeastern uinta basin utah u s a abstract the early to middle eocene green river formation consists of continental strata deposited in laramide ponded basins in utah colorado and wyoming this study 1 documents fluvial and lacustrine strata from the douglas creek and parachute creek members of the middle green river formation southeastern uinta basin utah and 2 uses new interpretations of the link between climate and fluvial sedimentary expression to interpret the terrestrial evolution of early eocene climate the stratigraphy was analyzed via outcrops along a 10 km transect in main canyon on the tavaputs plateau and is divided into three distinct stratigraphically separated depositional settings 1 the lowermost interval 1 is dominated by amalgamated sandstone channels that contain 70 100 upper flow regime sedimentary structures the channels are interpreted to represent fluvial deposits controlled by a highly seasonal climate where most deposition was limited to seasonal flooding events 2 interval 2 is dominated by alternating siliciclastic and carbonate lacustrine deposits interpreted as local pulsed fluvial siliciclastic input into shallow lake uinta and periods of fluvial quiescence represented by littoral carbonate deposition 3 the uppermost interval 3 is dominated by erosionally based trough cross bedded sandstone channels interbedded with littoral lacustrine and deltaic deposits the interval 3 sandstone channels are interpreted as perennial fluvial deposits with relatively little variation in annual discharge akin to modern humid temperate fluvial systems the stratigraphic transition from seasonally controlled interval 1 to perennial interval 3 fluvial deposits is interpreted to represent a fundamental shift in eocene climate from the peak hyperthermal regime of the early eocene climatic optimum eeco to a more stable post eeco climate

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

large scale mud diapirism as a record of late stage laramide tectonism within the eocene green river formation wyoming abstract the gruene and verde mud diapirs which range in size from 70 to 95 m in diameter are exposed within the wilkins peak member of the eocene green river formation near flaming gorge reservoir southwest wyoming these diapirs are sourced from the lower unit of the wilkins peak member lower middle and upper units can be defined based on dominant lithology and were emplaced into the upper unit of the wilkins peak member cross cutting hundreds of meters of strata the structures contain brecciated dolomicritic and lime mudstones with minor amounts of siliciclastic clays pervasive quartz veining is present throughout both diapirs though heavily disturbed original bedding can be seen in both localities either dipping radially outward towards the margins of the diapir as is dominant at the gruene diapir or tilted but near horizontal as is the dominant expression at the smaller verde diapir the gruene diapir can be seen in contact with several fluvial sandstone bodies within the upper wilkins peak strata in outcrop and these fluvial sandstones transition from regional near horizontal dips to steeply dipping beds and bedsets within 50 m of the diapir these sands show no signs of brittle deformation and dip ranges from 20 to 50 radially away from the center of the diapir to the north west and east where sands are observed these are interpreted here to have been deformed pre lithification at or near the surface by the rising mud diapir offering an important control on the timing of diapirism near the end of the early eocene deformation structures such as clastic dikes brecciation and convoluted bedding have been documented by others at or near this stratigraphic interval in utah wyoming and colorado and these smaller structures have been interpreted as seismites we suggest that these mud diapirs are a larger scale expression of this same seismic activity

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

detection quantification and significance of hiatuses in pelagic and hemipelagic strata temporal gaps in the stratigraphic record have important implications for the interpretation of stratigraphically rapid geochemical and paleobiologic changes for the development of high resolution time scales e g orbital time scales and for deciphering the response of depositional systems to climatic change and basin evolution e g accommodation space vs sediment supply in ancient pelagic and hemipelagic strata the identification of relatively short hiatus 10 3 10 6 years is commonly challenged by the resolution limits of geochronologic techniques in this study a quantitative method is developed to identify and quantify hiatuses in strata where milankovitch orbital cycles are documented the new method is based on the interpretation of evolutive harmonic analysis eha results and permits estimation of minimum durations for the temporal gaps application of this technique to an optical densitometry data series derived from the cenomanian turonian c t bridge creek limestone member permits quantification of hiatus within the unit and addresses important questions about abrupt changes in biogeochemical proxy records across the boundary interval integration of the new method with stratigraphic data and geochemical burial flux estimates permits a detailed reconstruction of the controls on sediment delivery and hiatus generation including a refined analysis of the orbital scale linkages between climate and sedimentation d 2004 elsevier b v all rights reserved

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

chronostratigraphic correlation of lacustrine deposits using 87sr 86sr ratios eocene green river formation wyoming u s a abstract the reconstruction of detailed basin scale depositional histories from sedimentary rocks fundamentally depends on the availability of reliable time markers unlike marine strata lacustrine strata typically lack rapidly evolving cosmopolitan fauna or flora that might serve this purpose depending on their geologic context lacustrine strata may also lack tephras that could provide isochronous markers or radioisotopic age variations in 87 sr 86 sr ratios could potentially provide an alternative means of chronostratigraphic correlation for carbonate rich lake deposits based on the hypothesis that sr isotopes are well mixed in a lake and do not experience significant fractionation to test this hypothesis we measured 87 sr 86 sr ratios in 114 samples from two drill cores of the upper wilkins peak member from the green river formation that are located 23 km apart these cores can be independently correlated using distinctive tephras and organic carbon rich mudstone horizons measured 87 sr 86 sr ratios range from 0 71154 to 0 71504 and vary inversely with lake water depth as interpreted by sedimentary lithofacies characteristics lower ratios of 87 sr 86 sr are found in lithofacies deposited during lake highstands which are marked by laminated dark gray mudstone and elevated organic carbon enrichment as measured by fischer assay analysis higher 87 sr 86 sr ratios occur in lithofacies deposited during lake lowstands which are marked by organic lean gray green mudstone 87 sr 86 sr in approximately time equivalent samples from the two cores show a strong positive correlation r 0 68 despite the likely presence of small temporal mismatches between approximately correlative samples we conclude that lake water was consistently well mixed with respect to sr across distances of at least 23 km these results suggest that 87 sr 86 sr can serve as a powerful tool to aid high resolution chronostratigraphic correlation of lake deposits

integrated quantitative stratigraphy of the cenomanian turonian bridge creek limestone member using evolutive harmonic analysis and stratigraphic modeling abstract secular changes in bulk sedimentation have a significant impact on the preservation of climatic signals in rhythmically bedded strata in this study a quantitative cyclostratigraphic methodology is developed to use these signal distortions as a means to reconstruct sedimentation the method exploits a moving window fourier technique that we designate evolutive harmonic analysis eha we calibrate this methodology to a specific set of geologic conditions i e changes in bulk sedimentation using a series of stratigraphic models and then apply the technique to the cenomanian turonian greenhorn formation of the western interior basin application of eha to strata that preserve a record of orbital forcing allows the reconstruction of a high resolution sedimentation history in which bulk sedimentation rates and hiatuses are quantified using the data on bulk sedimentation rate rates of accumulation for geochemical proxies representing detrital biogenic and authigenic contributions to the sediment can be calculated by integrating these quantitative assessments of siliciclastic dilution primary production and depositional redox conditions within a high resolution chronostratigraphic framework we are able to deconvolve secular trends in hemipelagic sedimentation during the late cenomanian early turonian in the western interior basin this integrated quantitative stratigraphic approach allows a reevaluation of hypotheses for the accumulation of excess organic matter in the western interior basin during the interval representing oceanic anoxic event ii

evolution of early cenozoic marine temperatures the equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals late paleocene early eocene early middle eocene late eocene and early oligocene paleotemperatures are calculated using standard oxygen isotope temperature equations with adjustments to account for 1 variations in sea water 18o related to changes in global ice volume over time and 2 latitudinal gradients in surface water 18o these reconstructions indicate that sea surface temperatures sst of the southern oceans in the early eocene were as high as 15 c whereas temperatures during the late paleocene and early middle eocene reached maximum levels of 10 12 c by the late eocene and early oligocene high latitude sst had declined to 6 and 4 c respectively for most of the early paleogene low latitude sub tropical temperatures remained constant and well within the range of holocene temperatures 24 ndash 25 c but by the late eocene and early oligocene declined to values in the range of 18 to 22 c the late paleogene apparent decline in tropical temperatures however might be artificial because of dissolution of near surface foraminifera tests which biased sediment assemblages toward deeper dwelling foraminifera moreover according to recent plate reconstructions it appears that the majority of sites upon which the late eocene and early oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling global deepwater temperature on average paralleled southern ocean sst for most of the paleogene we speculate based on the overall timing and character of marine sea surface temperature variation during the paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high latitude warmth of the early eocene

lake type controls on petroleum source rock potential in nonmarine basins based on numerous empirical observations of lacustrine basin strata we propose a three fold classification of lacustrine facies associations that accounts for the most important features of lacustrine petroleum source rocks and provides a predictive framework for exploration in nonmarine basins where lacustrine facies are incompletely delineated 1 the fluvial lacustrine facies association is characterized by freshwater lacustrine mudstones interbedded with fluvial deltaic deposits commonly including coal shoreline progradation dominates basin fill resulting in the stacking of indistinctly expressed cycles up to 10 m thick in map view the deposits may be regionally widespread but laterally discontinuous and contain strong facies contrasts transported terrestrial organic matter contributes to mixed type i iii kerogens that generate waxy oil type i kerogen is hydrogen rich and oil prone type iii kerogen is hydrogen poor and mainly gas prone the luman tongue of the green river formation wyoming and the honyanchi formation junggar basin china provide examples of this facies association which is also present in the songliao basin of northeastern china the central sumatra basin and the cretaceous doba doseo basins in west central africa 2 the fluctuating profundal facies association represents a combination of progradational and aggradational basin fill and includes some of the world s richest source rocks deposits are regionally extensive in map view having relatively homogenous source facies containing oil prone type i kerogen examples include the laney member of the green river formation wyoming the lucaogou formation junggar basin china the bucomazi formation offshore west africa and the lagoa feia formation campos basin brazil 3 the evaporative facies association represents dominantly aggradational fill related to desiccation cycles in saline to hypersaline lakes and may include evaporite and eolianite deposits sublittoral organic rich mudstone facies are relatively thin but may be begin page 1034 quite rich and widespread the highest organic enrichment coincides with the deepest lake stages low input of land plant organic matter results in minimal lateral contrasts in organic content in some cases a distinctive type i s sulfur rich kerogen may generate oil at thermal maturities as low as 0 45 vitrinite reflectance equivalent examples include the wilkins peak member of the green river formation wyoming the jingjingzigou formation junggar basin china the jianghan and qaidam basins china and the blanca lila formation argentina

a depth derived pleistocene age model uncertainty estimates sedimentation variability and nonlinear climate change 1 a new chronology of glaciation spanning the last 780 000 years is estimated from 21 marine sediment cores using depth as a proxy for time to avoid biasing this depth derived age estimate the depth scale is first corrected for the effects of sediment compaction to provide age uncertainty estimates the spatial and temporal variability of marine sediment accumulation rates are estimated and modeled as an autocorrelated stochastic process depth derived ages are estimated to be accurate to within 9000 years and within this uncertainty are consistent with the orbitally tuned age estimates nonetheless the remaining differences between the depth and orbitally tuned chronologies produce important differences in the spectral domain from the 18o record using the depth derived ages we infer that there are weak nonlinearities involving the 100 kyr and obliquity frequency bands which generate interaction bands at sum and difference frequencies if an orbitally tuned age model is instead applied these interactions are suppressed with the system appearing more nearly linear

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

climate driven paleolimnological change controls lacustrine mudstone depositional process and organic matter accumulation constraints from lithofacies and geochemical studies in the zhanhua depression eastern china abstract the influence of paleoclimate on the depositional process of lacustrine mudstone and organic matter accumulation is important to both paleoclimate reconstruction and hydrocarbon exploration here we study the lower third member es3l of the eocene shahejie formation in the zhanhua depression bohai bay basin eastern china in order to understand how paleoclimate influenced depositional processes and organic matter accumulation of lacustrine organic rich mudstone by combining detailed core descriptions and microscopic observations and high resolution mineralogical and geochemical analyses we identified two major lithofacies including massive calcareous mudstone and laminated calcareous mudstone from the luo 69 drilling core the sedimentologic observations and changes of geochemical proxies including detritus index ln al2o3 na2o b ga and v v ni suggest that the massive calcareous mudstone was deposited in a small shallow salt lake that was dysoxic anoxic and the paleoclimate in the lake catchment was cool and arid and the laminated calcareous mudstone was deposited in a large and deep stratified lake which has anoxic highly saline bottom and oxic less saline surface water and the lake catchment was more humid and warm the dominant lithofacies changed from laminated calcareous mudstone to massive calcareous mudstone in the studied core suggesting that the lake became shallower and smaller when the paleoclimate became cooler and drier through time such a climate trend may be a response to global cooling during the middle eocene the average total organic content toc in both lacustrine highstand and lowstand are comparable even though the lake water chemistry and amount of terrigenous input are different we infer that the accumulation of organic matter within the lacustrine highstand was controlled by the combination of primary productivity carbonate production and preservation in anoxic bottom water while accumulation within lacustrine lowstand was only controlled by primary productivity

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

resolving milankovitch consideration of signal and noise milankovitch climate theory provides a fundamental framework for the study of ancient climates although the identification and quantification of orbital rhythms are commonplace in paleoclimate research criticisms have been advanced that dispute the importance of an astronomical climate driver if these criticisms are valid major revisions in our understanding of the climate system and past climates are required resolution of this issue is hindered by numerous factors that challenge accurate quantification of orbital cyclicity in paleoclimate archives in this study we delineate sources of noise that distort the primary orbital signal in proxy climate records and utilize this template in tandem with advanced spectral methods to quantify milankovitch forced paced climate variability in a temperature proxy record from the vostok ice core vimeux and others 2002 our analysis indicates that vostok temperature variance is almost equally apportioned between three components the precession and obliquity periods 28 a periodic 100 000 year cycle 41 and the background continuum 31 a range of analyses accounting for various frequency bands of interest and potential bias introduced by the saw tooth shape of the glacial interglacial cycle establish that precession and obliquity periods account for between 25 percent to 41 percent of the variance in the 1 10 kyr 1 100 kyr band and between 39 percent to 66 percent of the variance in the 1 10 kyr 1 64 kyr band these results are approximately two to four times greater than those published by wunsch 2004 for the same vostok time series in all cases most of the remaining variance is accounted for by the 100 000 year cycle which is distinct from a background continuum that resembles autoregressive red noise our analysis high lights the importance of a comprehensive assessment of the climate signals in geologic records and underscores the significance of orbital forcing pacing as a primary agent of pleistocene climate change

lacustrine 87 sr 86 sr as a tracer to reconstruct milankovitch forcing of the eocene hydrologic cycle abstract the green river formation grf provides one of the premier paleoclimate archives of the early eocene climatic optimum 50 ma representing the apex of the early cenozoic greenhouse climate rhythmic lake level variability expressed in the grf has inspired numerous hypotheses for the behavior of the eocene hydrologic cycle including its linkage to astronomical forcing solar variability and the el nino southern oscillation enso however the lack of sufficient proxy data to document atmospheric water mass transport and the geographic pattern of evaporation precipitation runoff has made it difficult to discriminate between different models for astronomical forcing variable 87sr 86sr ratios of bedrock that encompass the grf provide an opportunity to reconstruct the spatial expression of the eocene hydrologic cycle and its linkage to lake level here sr isotope data from the wilkins peak member a rhythmic succession that has been demonstrated to record milankovitch forcing of lake levels indicate that high lake levels reflect an increased proportion of runoff from less radiogenic rocks west of the basin eliminating a number of the existing astronomical forcing hypotheses the 87sr 86sr variability is consistent with a change in mean enso state which is predicted by climate models to be linked to orbital insolation thus the 87sr 86sr data reveal a coupling of high frequency enso and low frequency astronomical climate variability and also predict the existence of sizable astronomically forced alpine snowpack during the last greenhouse climate more broadly this study demonstrates the utility of 87sr 86sr as a powerful tool for reconstructing the deep time hydrologic cycle