shoreline response to autogenic processes of sediment storage and release in the fluvial system 1 experimentally determined shoreline migration rates show high frequency autogenic variability superimposed on low frequency allogenic shoreline responses induced by eustatic base level change this variability persists even when the shoreline migration is averaged laterally indicating time variation in total sediment discharge reaching the shoreline the magnitude of autogenic variability in shoreline migration rate changes by roughly a factor of 3 depending on the shoreline migration direction it is strongest during transgression when the shoreline is on average migrating against the mean sediment flow and weakest during regression when the shoreline is migrating with the mean sediment flow we propose that this time variation is due to overall sediment storage and release in the fluvial system we use a one dimensional geometric model to model the autogenic signals observed in the experiment the model uses small periodic changes in the fluvial slope to represent the effects of storage and release of supplied sediment due to intrinsic variation in the transport efficiency of the fluvial system the periodic pulses of sediment discharge to the shoreline required in the model to explain the variations in shoreline migration can exceed by an order of magnitude the mean allogenic sediment discharge the slope variability required in the model to explain the autogenic shoreline signals is 1 4 of the mean slope this is well within the range of observed variability in depositional fluvial slopes we propose that at least part of this observed variability is real that is the long profile slope of a depositional river system may have an intrinsic elasticity of a few percent of its mean value even under steady forcing autogenic slope variation of this magnitude could readily produce parasequence scale deposits in the stratigraphic record

avulsions and the spatio temporal evolution of debris flow fans debris flows are water laden masses of sediment that move rapidly through channel networks and over alluvial fans where they can devastate people and property episodic shifts in the position of a debris flow channel termed avulsions are critical for debris flow fan evolution and for understanding flow hazards because avulsions distribute debris flow deposits through space and time however both the mechanisms of flow avulsion and their effects on the long term evolution of debris flow fans are poorly understood here we document and analyze the spatial and temporal patterns of debris flow activity obtained by repeat topographic analyses dendrogeomorphic and lichenometric reconstructions and cosmogenic radionuclide dating on 16 fans from japan usa switzerland france and kyrgyzstan where possible we analyze the observed spatio temporal patterns of debris flow activity in conjunction with high resolution topographic data to identify the main controls on avulsion we identify two main processes that control avulsions on debris flow fans operating over distinct time scales first during individual flows or flow surges deposition of sediment plugs locally blocks channels and forces subsequent flows to avulse into alternative flow paths plug deposition is a stochastic process but appears to depend in part on the sequence of flow volumes the geometry of the channel and the composition of the flows second over time scales of tens of events the average locus of debris flow deposition gradually shifts toward the topographically lower parts of a fan highlighting the importance of topographic compensation for fan evolution our documented debris flow avulsions often but not always follow a pattern of channel plugging backstepping of deposition toward the fan apex over one or more flows avulsion and establishment of a new active channel large flows can have contrasting impacts depending on whether or not they follow smaller flows that have deposited channel plugs these results suggest that avulsions and spatio temporal patterns of debris flow fan formation strongly depend on both the magnitude frequency distribution and the sequence of the flows feeding a fan while individual avulsions are generally abrupt and difficult to predict the presence of debris flow plugs and patterns of backstepping may be useful as indicators of impending avulsions over longer time scales the compensational tendency of flows to avulse into topographic depressions on the fan may also be used to identify sectors of the fan that are at risk of future inundation

constraining the early eocene climatic optimum a terrestrial interhemispheric comparison the early eocene climatic optimum was a period of major climatic and environmental change that was caused by perturbations to the global carbon cycle recent work from terrestrial sections in the northern hemisphere demonstrates that the period was characterized by different responses in the terrestrial and marine realms suggesting that traditional causal mechanisms may not adequately explain the dynamics of the early eocene climatic optimum here we present a new high resolution multiproxy record of terrestrial climatic and environmental conditions during the early eocene climatic optimum from the southern hemisphere and compare this reconstruction to other marine and terrestrial records similar to northern hemisphere terrestrial records there is a transient peak period of atmospheric carbon isotope enrichment as well as increased temperatures and precipitation which indicate that terrestrial environmental responses to the early eocene climatic optimum were broadly consistent in temperate settings worldwide this global consistency in terrestrial records demonstrates differences in peak warming time scales and carbon isotope responses between marine and terrestrial systems which further constrain potential causes for the early eocene climatic optimum to multiple system or nontraditional mechanisms and highlight the importance of paired records for understanding past climate

an empirical statistical model for debris flow travel distance an empirical model is presented for analysis of debris flows based on field observations of landslides from clear cuts in the queen charlotte islands british columbia given an initial failure volume changes in event magnitude arising from entrainment and deposition along the path of movement are used to establish the point at which the cumulative flow volume diminishes to zero and therefore the total travel distance hillslope morphology is used to assign three types of flow behaviour unconfined confined and transition flow flow behaviour and slope angle determine the occurrence of entrainment or deposition in the model for every reach of the event path volume change in a reach is calculated from regression analysis of the queen charlotte islands field observations predictor variables are reach length width of entrainment and or deposition and slope angle together with a bend angle function and the incoming flow volume key words slope stability debris flow travel distance runout ris

simplified process modeling of river avulsion and alluvial architecture connecting models and field data abstract modeling is an invaluable tool for studying sedimentary basin filling and for understanding depositional processes with long recurrence intervals including channel avulsion simplified modeling approaches such as cellular models and process analogue experiments are particularly useful for efficiently exploring alternative hypotheses and evaluating first order controls on river avulsion and alluvial architecture here we review the history and current state of the art in simplified avulsion and alluvial architecture models with a particular focus on how results and insights from these models can be incorporated into field and subsurface studies and vice versa simplified avulsion and alluvial architecture models have proliferated in the past decade providing a wide variety of models to serve as a basis for future coupled field modeling studies we compare features of leading models and discuss avenues for effectively pairing model capabilities with hypotheses and field data outstanding questions highlighted by recent modeling efforts include 1 what thresholds control avulsion initiation in different systems 2 how do floodplain processes and topography influence avulsion dynamics and alluvial architecture 3 what factors determine where avulsion channels stabilize answering these questions will require targeted modeling efforts coupled to data from ancient systems hence our model comparison emphasizes features that can be used to choose or design fit for purpose models and we outline how quantitative data useful for model selection and validation can be obtained from modern systems and ancient deposits matching model goals with targeted questions and model parameters and predictions with quantitative field data will help tighten communication between field and model oriented sedimentary geologists facilitating advances in our understanding of river avulsion and alluvial architecture

abrupt increase in seasonal extreme precipitation at the paleocene eocene boundary a prominent increase in atmospheric co at the paleocene eocene boundary ca 55 ma led to the warmest earth of the cenozoic for similar to 100 k y high resolution studies of continental flood plain sediment records across this boundary can provide crucial information on how the hydrological cycle responds to rapidly changing co2 here we show from continental records across the paleocene eocene boundary in the spanish pyrenees a subtropical paleosetting that during the early most intense phase of co2 rise normal semiarid coastal plains with few river channels of 10 200 m width were abruptly replaced by a vast conglomeratic braid plain covering at least 500 km 2 and most likely more than 2000 km 2 this braid plain is interpreted as the proximal parts of a megafan carbonate nodules in the megafan deposits attest to seasonally dry periods and together with megafan development imply a dramatic increase in seasonal rain and an increased intra annual humidity gradient the megafan formed over a few thousand years to similar to 10 k y directly after the paleocene eocene boundary only repeated severe floods and rainstorms could have contributed the water energy required to transport the enormous amounts of large boulders and gravel of the megafan during this short time span the findings represent evidence for considerable changes in regional hydrological cycles following greenhouse gas emissions less

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

erosion of steepland valleys by debris flows episodic debris flows scour the rock beds of many steepland valleys along recent debris flow runout paths in the western united states we have observed evidence for bedrock lowering primarily by the impact of large particles entrained in debris flows this evidence may persist to the point at which debris flow deposition occurs commonly at slopes of less than 0 03 0 10 we find that debris flow scoured valleys have a topographic signature that is fundamentally different from that predicted by bedrock river incision models much of this difference results from the fact that local valley slope shows a tendency to decrease abruptly downstream of tributaries that contribute throughgoing debris flows the degree of weathering of valley floor bedrock may also decrease abruptly downstream of such junctions on the basis of these observations we hypothesize that valley slope is adjusted to the long term frequency of debris flows and that valleys scoured by debris flows should not be modeled using conventional bedrock river incision laws we use field observations to justify one possible debris flow incision model whose lowering rate is proportional to the integral of solid inertial normal stresses from particle impacts along the flow and the number of upvalley debris flow sources the model predicts that increases in incision rate caused by increases in flow event frequency and length as flows gain material downvalley are balanced by rate reductions from reduced inertial normal stress at lower slopes and stronger less weathered bedrock these adjustments lead to a spatially uniform lowering rate although the proposed expression leads to equilibrium long profiles with the correct topographic signature the crudeness with which the debris flow dynamics are parameterized reveals that we are far from a validated debris flow incision law however the vast extent of steepland valley networks above slopes of 0 03 0 10 illustrates the need to understand debris flow incision if we hope to understand the evolution of steep topography around the world

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

dynamic controls on erosion and deposition on debris flow fans debris flows are among the most hazardous and unpredictable of surface processes in mountainous areas this is partly because debris flow erosion and deposition are poorly understood resulting in major uncertainties in flow behavior channel stability and sequential effects of multiple flows here we apply terrestrial laser scanning and flow hydrograph analysis to quantify erosion and deposition in a series of debris flows at illgraben switzerland we identify flow depth as an important control on the pattern and magnitude of erosion whereas deposition is governed more by the geometry of flow margins the relationship between flow depth and erosion is visible both at the reach scale and at the scale of the entire fan maximum flow depth is a function of debris flow front discharge and pre flow channel cross section geometry and this dual control gives rise to complex interactions with implications for long term channel stability the use of fan stratigraphy for reconstruction of past debris flow regimes and the predictability of debris flow hazards

antarctic subtropical humid episode at the paleocene eocene boundary clay mineral evidence clay mineral assemblages from east antarctica have been analyzed at high stratigraphic resolution 20 to 1 ka throughout the interval from 55 6 to 55 0 ma which includes the terminal paleocene isotopic excursion in ocean drilling program site 690b on maud rise lat 65 s in the weddell sea region changes in the clay associations reflect a major increase in chemical weathering caused by increased temperature and or rainfall in at least this sector of east antarctica for a brief 270 ka interval in the latest paleocene this represents the most intense warming known for the cenozoic this high latitude climatic episode is recorded synchronously by stable isotopes and clay minerals a progression is evident in the clay assemblages during the latest paleocene that apparently reflects changing relations between temperature and precipitation this sequence began with the interval of rapid temperature increase that marks the beginning of the oxygen isotopic excursion a brief increase in kaolinite at the inception of the excursion suggests a temporary increase in year round precipitation in antarctica in response to an increased continent to ocean temperature gradient this kaolinite spike was followed by almost total dominance by smectite for the remainder of the isotopic excursion 120 ka suggesting that warmer southern ocean surface temperatures of 18 to 22 c were associated with seasonal precipitation alternating wet and dry seasons claymineral variations on antarctica during the isotopic excursion reflect a tight coupling between oceanic and continental climate change immediately following the excursion at 55 22 ma kaolinite percentages increased to values similar to modern subtropical tropical areas for 150 ka a remarkable event for the antarctic abundant kaolinite suggests perennial rainfall and minimum soil temperatures of 15 c during at least part of the year the kaolinite increased during a time of lower southern ocean surface water temperatures suggesting increased atmospheric heat transport toward the poles a temporary change in atmospheric circulation is suggested from dominantly zonal to meridional

estimating rates of debris flow entrainment from ground vibrations debris flows generate seismic waves as they travel downslope and can become more dangerous as they entrain sediment along their path we present field observations that show a systematic relation between the magnitude of seismic waves and the amount of erodible sediment beneath the flow specifically we observe that a debris flow traveling along a channel filled initially with sediment 0 34 m thick generates about 2 orders of magnitude less spectral power than a similar sized flow over the same channel without sediment fill we adapt a model from fluvial seismology to explain this observation and then invert it to estimate the level of bed sediment and rate of entrainment beneath a passing series of surges our estimates compare favorably with previous direct measurements of entrainment rates at the site suggesting the approach may be a new indirect way to obtain rare field constraints needed to test models of debris flow entrainment

effects of debris flow magnitude frequency distribution on avulsions and fan development shifts in the active channel on a debris flow fan termed avulsions pose a large threat because new channels can bypass mitigation measures and cause damage to settlements and infrastructure recent but limited field evidence suggests that avulsion processes and tendency may depend on the flow size distribution which is difficult to constrain in the field here we investigate how the flow magnitude frequency distribution and the associated flow magnitude sequences affect avulsion on debris flow fans we created three experimental fans with contrasting flow size distributions 1 a uniform distribution 2 a steep double pareto distribution with many flows around the mean and a limited number of large flows and 3 a shallow double pareto distribution with fewer flows around the mean and more abundant large flows the fan formed by uniform flows developed through regular sequences of stepwise channelization backstepping of deposition toward the fan apex and avulsion over multiple flows in contrast the wide range of sizes in the double pareto distributions led to distinct avulsion mechanisms and fan evolution here large flows could overtop channels creating levee breaches that could initiate avulsion immediately or in subsequent events moreover sequences of small to moderately sized flows could deposit channel plugs triggering avulsion in the next large flow this mechanism was most common on the fan formed by a steep double pareto distribution but was rare on the fan formed by a shallow double pareto distribution where large flows were more frequent we infer that some flow size distributions are more likely to cause avulsions especially those that produce abundant sequences of small flows followed by a large flow critically avulsions in our experiments could occur by either large single events or over multiple flows this observation has important implications for hazard assessment on debris flow fans suggesting that attention should be paid to flowhistory as well as flow size

astronomical calibration of the paleocene time the first complete cyclic sedimentary successions for the early paleogene from drilling multiple holes have been retrieved during two odp expeditions leg 198 shatsky rise nw pacific ocean and leg 208 walvis ridge se atlantic ocean these new records allow us to construct a comprehensive astronomically calibrated stratigraphic framework with an unprecedented accuracy for both the atlantic and the pacific oceans covering the entire paleocene epoch based on the identification of the stable long eccentricity cycle 405 kyr high resolution x ray fluorescence xrf core scanner and non destructive core logging data from sites 1209 through 1211 leg 198 and sites 1262 1267 leg 208 are the basis for such a robust chronostratigraphy former investigated marine odp sites 1001 and 1051 and land based e g zumaia sections have been integrated as well the high fidelity chronology is the prerequisite for deciphering mechanisms in relation to prominent transient climatic events as well as completely new insights into greenhouse climate variability in the early paleogene we demonstrate that the paleocene epoch covers 24 long eccentricity cycles we also show that no definite absolute age datums for the k pg boundary or the paleocene eocene thermal maximum petm can be provided by now because of still existing uncertainties in orbital solutions and radiometric dating however we provide two options for tuning of the paleocene which are only offset by 405 kyr our orbitally calibrated integrated leg 208 magnetostratigraphy is used to revise the geomagnetic polarity time scale gpts for chron c29 to c25 we established a high resolution calcareous nannofossil biostratigraphy for the south atlantic which allows a much more detailed relative scaling of stages with biozones the re evaluation of the south atlantic spreading rate model features higher frequent oscillations in spreading rates for magnetochron c28r c27n and c26n

quantitative reconstruction of late holocene surface evolution on an alpine debris flow fan debris flow fans form a ubiquitous record of past debris flow activity in mountainous areas and may be useful for inferring past flow characteristics and consequent future hazard extracting information on past debris flows from fan records however requires an understanding of debris flow deposition and fan surface evolution field scale studies of these processes have been very limited in this paper we document the patterns and timing of debris flow deposition on the surface of the large and exceptionally active illgraben fan in southwestern switzerland we use terrain analysis radiocarbon dating of sediment fill in the illgraben catchment and cosmogenic 10be and 36cl exposure dating of debris flow deposits on the fan to constrain the temporal evolution of the sediment routing system in the catchment and on the fan during the past 3200 years we show that the fan surface preserves a set of debris flow lobes that were predominantly deposited after the occurrence of a large rock avalanche near the fan apex at about 3200 years ago this rock avalanche shifted the apex of the fan and impounded sediment within the illgraben catchment subsequent evolution of the fan surface has been governed by both lateral and radial shifts in the active depositional lobe revealed by the cosmogenic radionuclide dates and by cross cutting geometrical relationships on the fan surface this pattern of frequent avulsion and fan surface occupation provides field scale evidence of the type of large scale compensatory behavior observed in experimental sediment routing systems

a probabilistic sediment cascade model of sediment transfer in the illgraben we present a probabilistic sediment cascade model to simulate sediment transfer in a mountain basin illgraben switzerland where sediment is produced by hillslope landslides and rockfalls and exported out of the basin by debris flows and floods the model conceptualizes the fluvial system as a spatially lumped cascade of connected reservoirs representing hillslope and channel storages where sediment goes through cycles of storage and remobilization by surface runoff the model includes all relevant hydrological processes that lead to runoff formation in an alpine basin such as precipitation snow accumulation snowmelt evapotranspiration and soil water storage although the processes of sediment transfer and debris flow generation are described in a simplified manner the model produces complex sediment discharge behavior which is driven by the availability of sediment and antecedent wetness conditions system memory as well as the triggering potential climatic forcing the observed probability distribution of debris flow volumes and their seasonality in 2000 2009 are reproduced the stochasticity of hillslope sediment input is important for reproducing realistic sediment storage variability although many details of the hillslope landslide triggering procedures are filtered out by the sediment transfer system the model allows us to explicitly quantify the division into transport and supply limited sediment discharge events we show that debris flows may be generated for a wide range of rainfall intensities because of variable antecedent basin wetness and snowmelt contribution to runoff which helps to understand the limitations of methods based on a single rainfall threshold for debris flow initiation in alpine basins

debris flow volume quantile prediction from catchment morphometry estimation of the volumes of potential future debris flows is a key factor in hazard assessment and mitigation worldwide however there are few catchments for which detailed volume frequency information is available we 1 reconstructed volume frequency curves for 10 debris flow catchments in saline valley california usa from a large number of well preserved unmodified surficial flow deposits and 2 assessed the correlations between lobe volume quantiles and a set of morphometric catchment characteristics we found statistically significant correlations between lobe volume quantiles including median and maximum and catchment relief length planimetric distance from the fan apex to the most distant point along the watershed boundary perimeter and melton ratio relief divided by the square root of catchment area these findings show that it may be possible to roughly estimate debris flow lobe volume quantiles from basic catchment characteristics that can be obtained from globally available elevation data this may assist in design volume estimation for debris flow catchments where past flow volumes are otherwise unknown

paleosol based paleoclimate reconstruction of the paleocene eocene thermal maximum northern argentina abstract the paleocene eocene thermal maximum petm is a well documented relatively short lived warm episode in earth history previous studies completed on marine and continental strata spanning the petm have focused on understanding the magnitude of warming and other atmospheric changes these studies completed largely in the northern hemisphere report warming that ranged from 4 to 8 c above mean annual paleotemperatures prior to warming in this study paleosols in the salta basin northern argentina are used to reconstruct paleoprecipitation rates and mean annual paleotemperatures of the southern hemisphere from before during and after the petm carbon isotope data are used to 1 identify the horizon in which the petm and other eocene hyperthermals are recorded and 2 to interpret perturbations of the global carbon cycle during the petm at the height of the petm paleoprecipitation proxies indicate 1500 mm of annual rainfall and a temperature increase of 5 c from pre petm values carbon isotope data records three negative carbon isotope excursions during the petm in this region suggesting the possibility of three distinct rapid releases of isotopically depleted carbon into the ocean atmosphere system the results presented here are one of only a few paleoclimate reconstructions from continental sediments spanning the petm in the southern hemisphere

on the duration of the paleocene eocene thermal maximum petm 1 the paleocene eocene thermal maximum petm is one of the best known examples of a transient climate perturbation associated with a brief but intense interval of global warming and a massive perturbation of the global carbon cycle from injection of isotopically light carbon into the ocean atmosphere system one key to quantifying the mass of carbon released identifying the source s and understanding the ultimate fate of this carbon is to develop high resolution age models two independent strategies have been employed cycle stratigraphy and analysis of extraterrestrial helium heet both of which were first tested on ocean drilling program odp site 690 these two methods are in agreement for the onset of the petm and initial recovery or the clay layer main body but seem to differ in the final recovery phase of the event above the clay layer where the carbonate contents rise and carbon isotope values return toward background values here we present a state of the art age model for the petm derived from a new orbital chronology developed with cycle stratigraphic records from sites drilled during odp leg 208 walvis ridge southeastern atlantic integrated with published records from site 690 weddell sea southern ocean odp leg 113 during leg 208 five paleocene eocene p e boundary sections sites 1262 to 1267 were recovered in multiple holes over a depth transect of more than 2200 m at the walvis ridge yielding the first stratigraphically complete p e deep sea sequence with moderate to relatively high sedimentation rates 1 to 3 cm ka where a is years a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records on the scale of precession cycles with a total duration of the petm now estimated to be 170 ka the revised cycle stratigraphic record confirms original estimates for the duration of the onset and initial recovery but suggests a new duration for the final recovery that is intermediate to the previous estimates by cycle stratigraphy and heet

terrestrial records of a regional weathering profile at the paleocene eocene boundary in the williston basin of north dakota the orange zone within the bear den member of the golden valley formation williston basin north dakota represents a terrestrial weathering profile formed by intense pedogenesis during an ancient ca 55 ma global warming event referred to as the paleocene eocene thermal maximum distinctive features of the orange zone include 1 high abundances of kaolinite 2 a strongly leached character with a bright orange iron enriched horizon 3 poor organic carbon preservation and 4 ferric pans pisoliths at its basal contact equivalent to modern lateritic materials though conclusive evidence such as a distinctive paleocene eocene thermal maximum flora and or definitive carbon isotope excursion is lacking the stratigraphic succession of palynofloral datums preserved within the upper part of the bear den orange zone is similar to that associated with the later stages of other terrestrial paleocene eocene thermal maximum records from the u s western interior bulk 13 c org ratios decrease through the orange zone as well but the magnitude of this isotopic decrease is less than that of the carbon isotope excursion thus the collective evidence indicates that the early initial stages of the paleocene eocene thermal maximum are either preserved within the barren condensed interval of the lower orange zone or are missing altogether from the williston basin stratigraphy and that the orange zone likely developed during the later recovery stages of the paleocene eocene thermal maximum the williston basin records generally agree with the tenet that continental weathering intensified during the paleocene eocene thermal maximum moreover these records indicate that the paleohydrology of the basin varied markedly and that sequestration of terrestrial organic carbon was greatly reduced as this transient global warming event unfolded

stable isotope stratigraphy and paleoclimatology of the paleogene bighorn basin wyoming usa abstract climatic warming from the late paleocene into the early eocene had profound effects on atmospheric and marine circulation marine thermal gradients and benthic biota in addition marine carbon isotope values decreased substantially in both surface and deep waters because carbon is rapidly exchanged between reservoirs at the earth s surface such as marine surface water the atmosphere land plants and materials that obtain carbon from plants e g soil minerals and herbivores carbon isotope fluctuations provide time lines linking the marine and continental records we analyzed the carbon isotope composition of paleosol carbonates and mammalian tooth enamel from stratigraphic sections in northwestern wyoming carbon isotope correlation demonstrates that a short interval of extreme high latitude warming coincided precisely with the first appearance of several important modern mammalian orders in addition oxygen isotope analyses of fossils and paleosol carbonates provide information about climatic conditions on land in the paleogene we reconstructed the oxygen isotope composition of local meteoric water using biogenic minerals paleocene eocene meteoric water was significantly 18 o depleted indicating substantial loss of water vapor during its transport to the region soil temperature was calculated as a proxy for mean annual temperature assuming oxygen isotope equilibrium between soil carbonate and meteoric water calculated temperatures were plausible 10 25 c but highly variable prohibiting high resolution analysis of local temperature variations in response to global climatic warming

correlation between isotope records in marine and continental carbon reservoirs near the palaeocene eocene boundary changes in the isotope content of the large marine carbon reservoir can force shifts in that of the smaller carbon pools in the atmosphere and on land the carbon isotope compositions of marine carbonate sediments from the late palaeocene vary considerably exhibiting a sudden decrease close to the palaeocene eocene boundary which coincides with deep sea benthic extinctions1 and with changes in ocean circulation here we report that these fluctuations in the marine carbon isotope record are closely tracked by the terrestrial records provided by palaeosol carbonates and mammalian tooth enamel in using palaeosol carbonates to reconstruct the co2 content of the ancient atmosphere2 isotope shifts of this sort will have to be taken into account the sharp decrease in 13c 12c ratios in the late palaeocene provides a datum for precise correlation of marine and continental records and suggests that abrupt climate warming at this time may have played an important role in the evolution of land mammals

paleogene paleosols and changes in pedogenesis during the initial eocene thermal maximum big bend national park texas usa this paper tests the hypothesis that continental chemical weathering increased during the initial eocene thermal maximum ietm by comparing paleosols that formed before and during the event in western texas the chemical index of alteration cia was used to investigate the weathering of silicate minerals paleosols generated before the ietm have cia values ranging from 62 to 72 and cia values during the ietm range from 67 to 82 the cia values for pre initial eocene thermal maximum paleosols indicate moderate weathering conditions and cia values during the event indicate moderate to extreme weathering conditions the clay mineralogy of the paleosols is dominated by smectite and it is only within paleosols that formed during the ietm that there is a change there is a notable increase in the amount of kaolinite in one paleosol horizon that is associated with the carbon excursion in addition there is an increase in the translocation of clays and iron and an increase in the leaching of calcite and plagioclase in initial eocene thermal maximum paleosols the differences between soils that formed before and during the initial eocene thermal maximum indicate that chemical weathering did increase during this ancient global warming event the mechanism responsible for increased weathering is interpreted to be an increase in hydrolysis reactions caused by an increase in humidity and an increase of carbonic acid in the soil due to elevated co2 levels during the initial eocene thermal maximum documentation of an increase in chemical weathering during the initial eocene thermal maximum is significant because it may have served as a negative feedback to reduce atmospheric co2

the influence of debris flow rheology on fan morphology owens valley california we have investigated factors controlling the surface morphology of debris flow fans comprising the bajada along the western slope of owens valley california these fans have average slopes of 4 an extensive network of abandoned boulder lined channels rough undulatory surfaces near the range front and smooth distal surfaces field relationships and mechanical considerations indicate that the channels of the bajada are products of fluvial incision and not debris flow scour this is significant because detailed geomorphic maps indicate that the channels strongly influence the pattern of debris flow deposition the locus of debris flow deposition on a channelized fan surface is set by the interaction of debris flows with the channel system and is controlled by channel size channel gradient flow volume flow hydrograph and flow rheology debris flow behavior is most directly controlled by variations in bulk sediment concentration and its influence on flow rheology whereas low sediment concentration debris flows tend to smooth the surface of the lower fan spreading into thin sheets and filling channels and surface undulations repeated deposition of high sediment concentration debris flows produces the rugged topography of the upper fan the texture of the fan surface rough or smooth is determined by the relative volumetric importance of these two types of debris flow in addition channel avulsions and the associated long term shifting of depositional loci are driven by in channel deposition of debris flows with the highest sediment concentrations these debris flows therefore play a critical role in determining both the structure of the channel network and the long term pattern of deposition on the fan surface as a whole we infer that the frequency distribution of debris flow rheologies set by source terrain geology and hydrology is an important control on fan morphology

positive feedback and momentum growth during debris flow entrainment of wet bed sediment debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep debris mantled slopes the flows can then grow dramatically in size and speed as they entrain material from their beds and banks but the mechanism of this growth is unclear indeed momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged here we use data from large scale experiments to assess the entrainment of bed material by debris flows we find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows the increased pore pressure facilitates progressive scour of the bed reduces basal friction and instigates positive feedback that causes flow speed mass and momentum to increase if dryer bed sediment is entrained however the feedback becomes negative and flow momentum declines we infer that analogous feedbacks could operate in other types of gravity driven mass flow that interact with erodible beds the mechanisms by which debris flows acquire mass and momentum as they entrain material are unclear large scale experiments suggest that the pore pressure of wet bed sediment increases as the flow moves over the bed leading to reduced friction and progressive scouring of the base

climato environmental controls on clay mineralogy of the hettangian bajocian successions of the mecsek mountains hungary an evidence for extreme continental weathering during the early toarcian oceanic anoxic event abstract clay mineralogy has been successfully used in palaeoclimatic interpretation of jurassic rocks in the mecsek zone hungary the clay mineral assemblages of the hettangian sinemurian fluvial and shallow marine coal bearing siliciclastic rocks gresten facies mecsek coal and vasas marl formations comprise predominantly illite smectite i s mixed layer minerals illite ill and kaolinite kao with the presence of berthierine and or chlorite these clay mineral suites suggest a humid subtropical climate with short term climate changes of high and low rainfall and a high supply of terrigenous clastics to the basin in the pliensbachian part of the sequence studied which is composed of predominantly hemipelagic mudstones allgau facies with intercalations of redeposited sandstone and limestone bodies the hosszuheteny calcareous marl mecseknadasd sandstone and kecskehat limestone formations are predominantly made up of illite and very little kaolinite and i s mixed layer minerals kao ill 1 suggesting a humid climate and intense continental weathering possibly related to the oceanic anoxic event in contrast rocks of the bajocian komlo calcareous marl formation contain high proportions of i s mixed layer mineral and illite with sparse occurrence of kaolinite kao ill 0 or kao ill

constraining paleohydrologic change during the paleocene eocene thermal maximum in the continental interior of north america abstract quantifying the relationship between carbon cycle perturbations and the hydrologic cycle in the geologic past is crucial to accurately modeling how future anthropogenic carbon emissions and resulting radiative forcing might affect the hydrologic cycle interpreting changes in proxy records for insight into paleohydrologic change is complex and documented records of paleohydrologic response to past global warming are rare we use the relationship between two independent proxy records the stable isotope ratios of hydrogen in n alkanes and oxygen in tooth enamel of coryphodon to examine paleohydrologic change in the continental interior of north america during the paleocene eocene thermal maximum petm hyperthermal 56 ma the coryphodon 18o record allows us to infer shifts in surface water isotope values through time by applying an empirical relationship between tooth enamel and precipitation 18o values precipitation 18o values increase by 4 during the petm but n alkane hydrogen isotope ratios show no directional change during the petm we explore multiple hypotheses that could explain the differences between the isotope records including a change in apparent fractionation as a result of plant community change a shift in the slope of the local meteoric water line a change in the season of rainfall or a shift in the season of lipid production we model the changes that would be required to reconcile the isotope records for each hypothesis and evaluate the likelihood of each of the scenarios we posit that the most likely hypothesis for the observed differences between the isotope records is a change in either the season of rainfall or the season of lipid production during the petm

frequency and magnitude of debris flows on cheekye river british columbia abstract natural hazard and risk assessments are predicated on a detailed understanding of the relationship between frequency and magnitude of the hazardous process under investigation when information is sought from the deep past i e several thousand years continuous event records do not exist and the researcher has to rely on proxy data to develop the frequency magnitude f m model such work is often prohibitively expensive and few well researched examples for mass movement are available worldwide the cheekye fan is a desirable location for land development and has a depth and breadth of previous research unprecedented on any debris flow fan in canada we pursued two principal strains of research to formulate a reliable f m relationship the first focuses on stratigraphic analyses combined with radiometric dating and dendrochronology to reconstruct a comprehensive picture of holocene debris flow activity the second approach examines hydrological limitations of rock avalanche evolution into debris flows through either entrainment of saturated sediments or by failure of a landslide generated dam and upstream impoundment we thus hypothesize that debris flows from cheekye river can be separated into two quasi homogenous populations those that are typically triggered by relatively small debris avalanches slumps or rock falls or simply by progressive bulking of in stream erodible sediments and those that are thought to result from transformation of rock avalanches our work suggests that debris flows exceeding some 3 million m3 in volume are unlikely to reach the cheekye fan as a result of limited water available to fully fluidize a rock avalanche this analysis has also demonstrated that in order to arrive at reasonable estimates for the frequency and magnitude of debris flows on a complex alluvial fan significant multidisciplinary efforts are required without the significant precursor investigations and the additional efforts of this study life and property may be jeopardized or the design of debris flow mitigation may be subject to considerable and unquantifiable error

autogenic avulsion channelization and backfilling dynamics of debris flow fans alluvial fans develop their semi conical shape by quasi cyclic avulsions of their geomorphologically active sector from a fixed fan apex on debris flow fans these quasi cyclic avulsions are poorly understood partly because physical scale experiments on the formation of fans have been limited largely to turbidite and fluvial fans and deltas in this study debris flow fans were experimentally created under constant extrinsic forcing and autogenic sequences of backfilling avulsion and channelization were observed backfilling avulsion and channelization were gradual processes that required multiple successive debris flow events debris flows avulsed along preferential flow paths given by the balance between steepest descent and flow inertia in the channelization phase debris flows became progressively longer and narrower because momentum increasingly focused on the flow front as flow narrowed resulting in longer run out and deeper channels backfilling commenced when debris flows reached their maximum possible length and channel depth as defined by channel slope and debris flow volume and composition after which they progressively shortened and widened until the entire channel was filled and avulsion was initiated the terminus of deposition moved upstream because the frontal lobe deposits of previous debris flows created a low gradient zone forcing deposition consequently the next debris flow was shorter which led to more in channel sedimentation causing more overbank flow in the next debris flow and resulting in reduced momentum to the flow front and shorter runout this topographic feedback is similar to the interaction between flow and mouth bars forcing backfilling and transitions from channelized to sheet flow in turbidite and fluvial fans and deltas debris flow avulsion cycles are governed by the same large scale topographic compensation that drives avulsion cycles on fluvial and turbidite fans although the detailed processes are unique to debris flow fans this novel result provides a basis for modelling of debris flow fans with applications in hazards and stratigraphy

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

an alternative age model for the paleocene eocene thermal maximum using extraterrestrial 3he a continuous age model for the brief climate excursion at the paleocene eocene boundary has been constructed by assuming a constant flux of extraterrestrial 3he 3he et to the seafloor 3he et measurements from odp site 690 provide quantitative evidence for the rapid onset few kyr and short duration 120 kyr of global warming and of the associated disturbance to the earth s surficial carbon budget at this time these observations support astronomically calibrated age models indicating extremely rapid release of isotopically light carbon possibly from seafloor methane hydrate as the proximal cause of the event however the 3he et technique indicates a previously unrecognized and extreme increase in sedimentation rate coincident with the return of climate proxies to pre event values the 3he et based age model thus suggests a far more rapid recovery from the climatic perturbation than previously proposed or predicted on the basis of the modern carbon cycle and so may indicate additional or accelerated mechanisms of carbon removal from the ocean atmosphere system during this period 3he et was also measured at odp site 1051 to test the validity of the site 690 chronology comparison of these data sets seems to require removal of several tens of kyr of sediment within the climatic excursion at site 1051 an observation consistent with sediment structures and previous age modeling efforts the site 1051 age model shows a 30 kyr period in which climate proxies return toward pre event values after which they remain invariant for 80 kyr if this rise represents the recovery interval identified at site 690 then the 3he et based age models of the two sites are in good agreement however alternative interpretations are possible and work on less disrupted sites is required to evaluate the reliability of the proposed new chronology of the climate excursion regardless of these details this work shows that the 3he et technique can provide useful independent evidence for the development and testing of astronomically calibrated age models

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

the paleocene eocene thermal maximum record in the organic matter of the claret and tendruy continental sections south central pyrenees lleida spain abstract the carbon isotope excursion cie associated with the paleocene eocene thermal maximum petm has been detected for the first time in the total organic carbon toc contained within the continental sediments of the tremp formation south central pyrenees lleida spain the 13 c toc magnitude of the cie is 4 3 in the claret section and 3 0 in the tendruy section with minimum values of 27 6 and 26 7 respectively previous studies have detected the cie in the south central pyrenees in both marine carbonates and within continental soil carbonate nodules these studies have located the onset of the cie either above or within the claret conglomerate interpreted as a megafan produced by a profound change in the precipitation regimen at the beginning of the petm our higher resolution 13 c toc study in the claret and tendruy sections places the onset of the cie below the base of the claret conglomerate and therefore suggests a 4 to 9 kyr time lag between the onset of the cie and an increase in intense seasonal precipitation rates furthermore this study suggests that the cie took place 30 55 kyr after the deposition of important late cernaysian tremp mammalian sites claret 4 tendruy v tendruy and palau which contain the youngest known occurrence of endemic paleocene mammalian taxa in europe before the mammalian dispersal event mde migration of new mammal groups such as perissodactyls artiodactyls primates marsupials carnivores creodonts and rodents the first immigrant mammals in europe are recorded at dormaal belgium above a hiatus the base of which has been dated to around the start of the cie our data indicate that the mde might have in fact occurred in europe within a time interval of about 67 kyr around the cie onset

palaeoclimatic significance of changes in clay mineralogy across the jurassic cretaceous boundary in england and france abstract clay mineralogical changes across the jurassic cretaceous boundary from the northern to the southern part of western europe show similar patterns in the mudrocks exposed on the yorkshire coast the paralic sediments of the dorset wessex basin and the jura and vocontian trough of s e france this comprises a change from smectite poor sediments in the jurassic with correspondingly abundant illite and kaolinite to sediments with abundant smectite in the jurassic cretaceous boundary beds depleted in kaolinite this change occurs in the oxfordian in the south to latest volgian in the north of the study area kaolinite reappears in abundance in the late ryazanian or stratigraphic equivalent in all the locations studied comparison with other climatic indicators and other areas suggest that these variations can be ascribed to a phase of latest jurassic earliest cretaceous aridity the onset of which appears to be diachronous across w europe possible causes for the climatic change towards aridity are examined the orographic effect of mountains or plateaus to the east of the study area is considered most likely

experimental study of debris flow entrainment over stepped gradient beds incorporating bed sediment porosity abstract the incorporation of bed sediment by a natural debris flow can cause significant growth in its size and destructive potential in this study the erosion features of debris flows in channels with stepped gradient beds were determined based on field observations and flume experiments field investigations revealed that channel sections with abrupt bed slope variations were eroded more intensely than others a series of small scale flume tests were conducted to study the pore pressure variations in erodible bed sediment and the basal entrainment behaviour of debris flows in channels with stepped gradients reference tests on a uniform bed slope demonstrate that inflection points in the bed longitudinal profile greatly alter the debris mixture flow pattern and accelerate entrainment pore pressure generation in the bed sediment supports debris flow entrainment by reducing basal friction peak pore pressures at concave sites were approximately two times higher than those observed at convex sites likely due to large changes in debris flow dynamics and intense interactions between the flow mixture and bed sediment low bed sediment porosities will increase the interlocking of grain particles promote the formation of clusters and enhance the strength of the grain skeleton suppressing basal entrainment in the flume tests lower peak pore pressures were observed as bed porosity decreased possibly due to fewer connecting channels for pore fluid pressure to transmit in the compacted bed sediment dimensionless analysis indicates that pore pressure fluctuations in the bed sediment were mainly generated by the overriding debris flow a new entrainment formula of debris flow over stepped gradient beds is proposed based on flume tests and theoretical analyses which may aid future debris flow modelling and hazard assessments

spheroids at the cretaceous tertiary boundary are altered impact droplets of basaltic composition sand size spheroids of k feldspar in the cretaceous tertiary c t boundary clay at caravaca southern spain were interpreted by smit and klaver as having solidified from a melt resulting from the impact of a large extraterrestrial body sand size spheroids of k feldspar glauconite and magnetite quartz have been found in the c t boundary clay in northern italy and spheroids of k feldspar and pyrite were found in the boundary clay at deep sea drilling project site 465a in the central pacific these spheroids have textures similar to those of rapidly crystallized feldspar and mafic silicates they are interpreted as diagenetically altered microcrystalline spherules of basaltic composition produced by the impact of a large asteroid in an ocean basin at the end of the cretaceous they are analogous to the glassy microtektites produced by impacts on more siliceous target rocks 21 references 4 figures

direct measurement of channel erosion by debris flows illgraben switzerland 1 the timing and magnitude of channel bed erosion by three debris flows was measured in 2008 at the illgraben catchment switzerland using a scour sensor which consisted of a vertical array of erodible sensor elements during the largest debris flow sediment was entrained progressively and stepwise at the flow head within 20 s after front arrival and onset of erosion started before maximum values for flow height and normal and shear stress measured nearby were reached erosion in one of the two smaller debris flows also occurred at the head of the flow but the magnitude of erosion was at the detection limit for the sensor for the other small debris flow we were not able to determine the timing of erosion due to the presence of a sediment layer covering the sensors measurements of pressure fluctuations along the channel sidewall which are produced by interparticle collisions within the flow indicate that the entrainment of sediment is coincident with the largest mean and fluctuating pressures suggesting that interparticle collisions may drive the erosion process at the front of debris flows after erosion at the head of the debris flows sediment was deposited on top of the erosion sensor columns indicating that the bed was reworked to a larger depth than directly visible at the surface after the event observations from elsewhere along the channel support our measurements of the magnitude of net debris flow erosion and indicate that significant erosion can be expected on debris fans when the flow is confined to a channel debris flow entrainment and subsequent bulking of the flow influence the flow dynamics and therefore should be considered in debris flow models and hazard assessment

autogenic response of alluvial bedrock transition to base level variation experiment and theory 1 short term autogenic processes are thought to be averaged out by long term allogenic forcing and have often been ruled out in stratigraphic interpretation it is generally difficult to resolve the scale of autogenic effects on landscape evolution and even more so on sedimentary records here we analyze short term variation in migration rate of the alluvial bedrock transition in a series of experiments the experiments developed a fan delta over a stationary sloped nonerodible basement with constant water and sediment discharges the rate of base level change varies between experiments but was constant for a given experiment the location of the alluvial bedrock transition varied autogenically in all experiments the instantaneous migration rate of the alluvial bedrock transition varied by as much as an order of magnitude more than that induced by allogenic forcing the strong autogenic pulses can be explained by sediment storage and release due to intrinsic variation in the transport efficiency of the fluvial system data from experiments with base level change indicate that the autogenic signal in the migrating alluvial bedrock transition is weakest during landward migration onlap when base level rises and strongest during basinward migration valley incision when base level falls we use a one dimensional geometric model to explain the variations in the autogenic response of the alluvial bedrock transition as a function of direction of base level change the model periodically changes fluvial slope to represent the effects of sediment storage and release with base level rise and fall the modeling result reproduces the observed pattern of autogenic variation in alluvial bedrock transition

limits of sediment transfer in an alpine debris flow catchment illgraben switzerland abstract the 9 5 km 2 illgraben catchment located in the rhone valley in the central alps of switzerland is one of the most active debris flow torrents in the alps in this paper we present sediment yield data collected in 2006 for segments where hillslopes and channels form a fully connected network and contrast these with sediment yields measured for disconnected hillslopes the data reveal that sediment yields are 1 2 orders of magnitude larger in segments where hillslopes are connected with the channel network than on disconnected hillslopes support for this conclusion is provided by observations made on 1959 1999 and 2004 aerial photographs that the vegetation cover in the disconnected segments is still intact whereas denudation rates of several centimeters per year in the connected segments have inhibited the establishment of a stable vegetation cover furthermore sediment supplied from hillslopes during the past 40 years has temporarily accumulated along the illgraben channel indicating that the channel aggraded over this period and has not yet recovered an implication of this observation is that initiation of debris flows in the illgraben catchment is limited more by the availability of intense rainfall than sediment in contrast on disconnected hillslopes sediment flux does not appear to be driven by precipitation the petrographic composition of the illgraben fan deposits indicates two distinct sediment sources one related to rockfall and the other to landslides and debris flows the presence of clasts from both sources implies multiple processes of erosion deposition mixing and re entrainment in the catchment before the material is exported to the illgraben fan and to the rhone river in addition delivery of large amounts of coarse grained sediment to the rhone causes a modification of the flow pattern from meandering or anastomosing upstream to braided downstream hence the direct connectivity between hillslope and channelized processes in the illgraben catchment causes not only rapid topographic modifications in the catchment but also morphologic adjustment in the rhone valley downstream

magnitude frequency relationships of debris flows and debris avalanches in relation to slope relief abstract probability of occurrence hazard intensity and encounter probability are key parameters in the quantitative risk analysis qra of landslides all are strongly dependent on magnitude of the landslides as a result magnitude frequency analysis should be a part of qra deriving representative magnitude frequency relationships for debris avalanches and debris flows however is difficult one key problem is illustrated with the example of a unique database from the coastal region of british columbia canada which was compiled entirely from detailed ground investigations the magnitude of debris avalanches and debris flows is not an independent statistical quantity but a function of the scale of a given slope as characterized by the slope length thus attempting to derive probability and magnitude for a given location or sub region from a regionally derived magnitude frequency curve may lead to incorrect predictions the same problem is pertinent to the application of the same approach to any type of landslide in which the largest combined dimension of the source volume including entrainment is of the same order as the length of the slope it is recommended that greater emphasis be placed on site specific geological observations at the expense of generalized statistics

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

clay mineral assemblages and analcime formation in a palaeogene fluvial lacustrine sequence maiz gordo formation palaeogen from northwestern argentina abstract the palaeogene maiz gordo formation is one of the main lacustrine events recorded in northwestern argentina it consists of sandstone mudstone and limestone beds 200 m thick deposited in a brackish alkaline lake and braided alluvial systems the maiz gordo lake evolved mainly as a closed system with brief periods as an open one x ray diffraction xrd and scanning electron microscopy sem were used to study samples from seven sites corresponding respectively to proximal intermediate and transitional positions of the fluvial environment and marginal and inner lake environment focusing on the clay mineralogy and analcime formation the basinward zonation of diagenetic minerals identified in the maiz gordo lake was mordenite analcime k feldspar although not a typical zonation of saline alkaline lakes it does indicate an increase in salinity and alkalinity towards the centre in proximal fluvial settings smectite predominates at the base of the sequence with scarce kaolinite towards the top a striking increase in kaolinite content suggests a change from a relatively arid climate with alternating humid and dry seasons towards a warm and humid climate kaolinite content clearly decreases in a basinward direction such a variation is attributable to changes in hydro geochemistry denoting the progressive influence of the brackish and alkaline lake water on interstitial pores sem images of intermediate fluvial samples reveal authigenesis of illite at the expense of kaolinite booklets in littoral and inner lake settings the clay fraction is composed of muscovite sometimes with subordinate smectite analcime occurs in variable amounts in all sedimentary facies in rock pores or filling veins it forms subhedral square to hexagonal or anhedral rounded crystals denoting that they coarsened at low to moderate degrees of supersaturation although the mordenite identified in a fluvial level would have been the precursor of analcime in the maiz gordo basin no textural evidence of analcime formation through replacement of mordenite or other precursor zeolite was found hence it is more probable that analcime formation took place by direct authigenic precipitation or through the reaction between interstitial brines and clay minerals or plagioclase

evidence of cyclic climatic changes recorded in clay mineral assemblages from a continental paleocene eocene sequence northwestern argentina abstract the continental paleocene eocene sequence investigated in this study belongs to the salta group deposited in an intracontinental rift the salta basin nw argentina that evolved from the lower cretaceous to the middle paleogene and is subdivided into the pirgua the balbuena and the santa barbara subgroups the maiz gordo formation 200 m thick is the middle unit of the santa barbara subgroup deposited during late post rift sedimentation we studied the mineralogy of fine grained horizons of this formation by x ray diffraction and scanning electron microscopy sem in order to examine the connection between vertical changes in clay mineralogy in alluvial sediments and paleosols and global paleoclimatic changes registered during the paleogene paleosols vary from calcic vertisols in the lowermost levels to inseptisols and gleysols in intermediate positions to gleyed oxisols in the upper section indicating increased chemical weathering through time clay mineral relative abundances vary with a general increase in kaolinite content from bottom to top however at one site there are significant variations in kaolinite muscovite kln ms that define five cycles of kaolinite abundance and kln ms that indicate cyclic patterns of paleoprecipitation and paleotemperature these are interpreted as several short lived hyperthermals during the paleocene early eocene in the southern hemisphere which correlate with well established episodes of warmth documented from the northern hemisphere

comparison of clay mineral stratigraphy to other proxy palaeoclimate indicators in the mesozoic of nw europe this paper reviews the opportunities and pitfalls associated with using clay mineralogical analysis in palaeoclimatic reconstructions following this conjunctive methods of improving the reliability of clay mineralogical analysis are reviewed the mesozoic succession of nw europe is employed as a case study this demonstrates the relationship between clay mineralogy and palaeoclimate proxy analyses may be integrated with clay mineralogical analysis to provide an assessment of aridity humidity contrasts in the hinterland climate as an example the abundance of kaolinite through the mesozoic shows that while interpretations may be difficult the mesozoic climate of nw europe was subject to great changes in rates of continental precipitation we may compare sedimentological facies mineralogy geochemistry indicators of palaeoprecipitation with palaeotemperature estimates the integration of clay mineralogical analyses with other sedimentological proxy indicators of palaeoclimate allows differentiation of palaeoclimatic effects from those of sea level and tectonic change we may also observe how widespread palaeoclimate changes were whether they were diachronous or synchronous how climate sea level and tectonics interact to control sedimentary facies and what palaeoclimate indicators are reliable

field measurement of basal forces generated by erosive debris flows 1 it has been proposed that debris flows cut bedrock valleys in steeplands worldwide but field measurements needed to constrain mechanistic models of this process remain sparse due to the difficulty of instrumenting natural flows here we present and analyze measurements made using an automated sensor network erosion bolts and a 15 24 cm by 15 24 cm force plate installed in the bedrock channel floor of a steep catchment these measurements allow us to quantify the distribution of basal forces from natural debris flow events that incised bedrock over the 4 year monitoring period 11 debris flow events scoured the bedrock channel floor no clear water flows were observed measurements of erosion bolts at the beginning and end of the study indicated that the bedrock channel floor was lowered by 36 to 64 mm the basal force during these erosive debris flow events had a large magnitude up to 21 kn which was approximately 50 times larger than the concurrent time averaged mean force high frequency greater than 1 hz fluctuating component we interpret these fluctuations as flow particles impacting the bed the resulting variability in force magnitude increased linearly with the time averaged mean basal force probability density functions of basal normal forces were consistent with a generalized pareto distribution rather than the exponential distribution that is commonly found in experimental and simulated monodispersed granular flows and which has a lower probability of large forces when the bed sediment thickness covering the force plate was greater than 20 times the median bed sediment grain size no significant fluctuations about the time averaged mean force were measured indicating that a thin layer of sediment 5 cm in the monitored cases can effectively shield the subjacent bed from erosive impacts coarse grained granular surges and water rich intersurge flow had very similar basal force distributions despite differences in appearance and bulk flow density these results demonstrate that debris flows can have strong control on rates of steepland evolution and contribute to a foundation needed for modeling debris flow incision stochastically

evolution of a natural debris flow in situ measurements of flow dynamics video imagery and terrestrial laser scanning many theoretical and laboratory studies have been undertaken to understand debris flow processes and their associated hazards however complete and quantitative data sets from natural debris flows needed for confirmation of these results are limited we used a novel combination of in situ measurements of debris flow dynamics video imagery and pre and postflow 2 cm resolution digital terrain models to study a natural debris flow event our field data constrain the initial and final reach morphology and key flow dynamics the observed event consisted of multiple surges each with clear variation of flow properties along the length of the surge steep highly resistant surge fronts of coarse grained material without measurable pore fluid pressure were pushed along by relatively fine grained and water rich tails that had a wide range of pore fluid pressures some two times greater than hydrostatic surges with larger nonequilibrium pore fluid pressures had longer travel distances a wide range of travel distances from different surges of similar size indicates that dynamic flow properties are of equal or greater importance than channel properties in determining where a particular surge will stop progressive vertical accretion of multiple surges generated the total thickness of mapped debris flow deposits nevertheless deposits had massive vertically unstratified sedimentological textures

gpr derived architecture of a lahar generated fan at cotopaxi volcano ecuador the internal geometry of volcaniclastic fans produced by aggradation during lahar events is difficult to examine in modern settings because of the frequent lack of three dimensional exposures this makes it challenging to i reconstruct the spatial and temporal evolution of such fans and ii interpret observed facies stratigraphy in the context of lahar flow dynamics from proximal to distal fan reaches this research therefore presents the results of a ground penetrating radar gpr survey of the rumipamba fan at the mouth of the burrohuaycu quebrada on the southwestern flank of cotopaxi volcano a survey grid consisting of 50 individual gpr profiles representing a total length of 19 4 km was constructed covering most of the 4 km2 large fan surface all gpr profiles were collected using a pulseekko 100 with a 400 v transmitter fan sediments consist of sandy and gravelly lahar deposits alternating with volcanic fallout including ash and pumice lapilli at times reworked by fluvial processes deposits could be ground truthed to a depth of 3 m whereas gpr penetration depth reaches 15 m data interpretation was based on classification into 15 distinct radar facies characterized by the nature of their bounding surfaces and or internal features cross referenced where possible with shallow exposures three main facies were identified parallel irregular and clinoform erosional contacts were distinguished from aggradational ones vertical channel fill and lateral accretion flow parallel versus flow transverse and proximal distal variations in deposit architecture were featured the results of this study confirm the existence of two major channel systems in the northern and southern extremities of the fan and the more recent formation of a smaller central fan channel system deposit architecture is complex and facies chronologies illustrate that lahars have affected the entire survey area

comment on paleosol based paleoclimate reconstruction of the paleocene eocene thermal maximum northern argentina by andrews e white t and del papa c palaeogeography palaeoclimatology palaeoecology v 471 p 181 195 abstract andrews et al 2017 present a paleosol based paleoclimate reconstruction of the paleocene eocene thermal maximum from localities in northern argentina we suggest that the age model presented for these localities is incorrect based on recently published magnetostratigraphy from the area and that the studied maiz gordo and lumbrera formations instead represent a paleoclimate record of the early to middle eocene this record combined with previously published data from these formations provide a more comprehensive regional reconstruction of paleoclimate and paleoenvironmental conditions during the peak of early eocene warmth including the early eocene climatic optimum and possibly the middle eocene climatic optimum

anthropogenic carbon release rate unprecedented during the past 66 million years carbon release rates during the palaeocene eocene thermal maximum are difficult to constrain comparing relative rates of carbon cycle and climate change at the event s onset suggests emissions were much slower than anthropogenic emissions

constraints on the numerical age of the paleocene eocene boundary here we present combined radio isotopic dating u pb zircon and cyclostratigraphic analysis of the carbon isotope excursion at the paleocene eocene p e boundary in spitsbergen to determine the numerical age of the boundary incorporating the total uncertainty from both radio isotopic and cyclostratigraphic datasets gives an age ranging from 55 728 55 964 ma within error of a recently proposed astronomical age of 55 93 ma combined with the assumption that the paleocene epoch spans twenty five 405 kyr cycles our new age for the boundary suggests an age of 66 ma for the cretaceous paleogene k pg boundary furthermore our p e boundary age is consistent with the hypothesis that the onset of the paleocene eocene thermal maximum petm at the boundary occurred on the falling limb of a 405 kyr cycle suggesting the event was initiated by a different mechanism to that which triggered the other early eocene hyperthermals

terrestrial evidence for a two stage mid paleocene biotic event abstract marine records of the paleocene indicate a series of hyperthermal events characterized by significant climatic and carbon cycle variability but there are few comparable continental records the mid paleocene biotic event mpbe is a recently described interval defined by a rapid negative carbon isotope excursion and major short term changes in marine ecosystems but it is as yet unclear whether the event was globally important here we present the first terrestrial paleoenvironmental record of the mpbe based on paleosols that document rapid and short lived increases in temperature and precipitation and resultant shifts in plant assemblages concomitant with substantial carbon isotope excursions the new record indicates that carbon cycle changes during the early late paleocene may have resulted in a two stage transient hyperthermal event that caused a significant perturbation to both the regional climate and terrestrial ecology of south america in addition to the major biotic event mpbe previously recognized in marine records overall this suggests that the mpbe may have been a global climate event with far reaching environmental impacts in both the marine and terrestrial realms

initiation and flow conditions of contemporary flows in martian gullies understanding the initial and flow conditions of contemporary flows in martian gullies generally believed to be triggered and fluidized by co2 sublimation is crucial for deciphering climate conditions needed to trigger and sustain them we employ the ramms rapid mass movement simulation debris flow and avalanche model to back calculate initial and flow conditions of recent flows in three gullies in hale crater we infer minimum release depths of 1 0 1 5 m and initial release volumes of 100 200 m3 entrainment leads to final flow volumes that are 2 5 5 5 times larger than initially released and entrainment is found necessary to match the observed flow deposits simulated mean cross channel flow velocities decrease from 3 4 m s 1 to 1 m s 1 from release area to flow terminus while flow depths generally decrease from 0 5 1 m to 0 1 0 2 m the mean cross channel erosion depth and deposition thicknesses are 0 1 0 3 m back calculated dry coulomb friction ranges from 0 1 to 0 25 and viscous turbulent friction between 100 200 m s 2 which are values similar to those of granular debris flows on earth these results suggest that recent flows in gullies are fluidized to a similar degree as are granular debris flows on earth using a novel model for mass flow fluidization by co2 sublimation we are able to show that under martian atmospheric conditions very small volumetric fractions of co2 of 1 within mass flows may indeed yield sufficiently large gas fluxes to cause fluidization and enhance flow mobility

a change from warm humid to cold dry climate conditions recorded in lower barremian clay dominated continental successions from the se iberian chain ne spain abstract a combined facies and clay mineralogy analysis of the continental succession recorded in the lower part of the blesa formation early barremian oliete subbasin ne spain allowed us to specify the palaeoclimatic and palaeoenvironmental conditions under which this sedimentary record originated six outcrops including clays clays marls and dm thick interbedded palustrine lacustrine limestone levels were logged and sampled for x ray diffraction and optical and electron microscopy analysis the lower levels consist of red clays with abundant ferruginous pisoids 1 5 mm in size and macropisoids 5 mm whereas the intermediate and upper levels are ochre and violet clays marls with few or no pisoids the pisoids normally consist of a nucleus and a cortex made up of several layers some pisoids have a fragment of a previous pisoid acting as a nucleus indicating local re working processes both the nucleus and the cortex are formed by hematite goethite variable contents of kaolinite and minor proportions of ilmenite their texture and mineralogy show an in situ growth interbedded limestone beds within the clay and clay marl dominated levels are formed by micrite microsparite and sparite these limestones are cemented by kaolinite and they also have pisoids indicating the occurrence of edaphic processes the red clays have the lowest calcite content and the highest hematite anatase diaspore goethite and kaolinite content by contrast the ochre and violet clays marls have higher illite content smectite is only detected in the ochre clays marls this mineral association is characteristic of lateritic palaeosols formed under warm and humid conditions kaolinite and smectite textures indicate that they are authigenic whereas illite may be of detrital origin the upward decrease in kaolinite hematite anatase diaspore and goethite content along with the increase in quartz content and the presence of smectite and illite reflect a change from warm and humid conditions to drier and colder conditions during the early barremian in the studied area

cenozoic climate changes a review based on time series analysis of marine benthic δ18o records the climate during the cenozoic era changed in several steps from ice free poles and warm conditions to ice covered poles and cold conditions since the 1950s a body of information on ice volume and temperature changes has been built up predominantly on the basis of measurements of the oxygen isotopic composition of shells of benthic foraminifera collected from marine sediment cores the statistical methodology of time series analysis has also evolved allowing more information to be extracted from these records here we provide a comprehensive view of cenozoic climate evolution by means of a coherent and systematic application of time series analytical tools to each record from a compilation spanning the interval from 4 to 61 myr ago we quantitatively describe several prominent features of the oxygen isotope record taking into account the various sources of uncertainty including measurement proxy noise and dating errors the estimated transition times and amplitudes allow us to assess causal climatological tectonic influences on the following known features of the cenozoic oxygen isotopic record paleocene eocene thermal maximum eocene oligocene transition oligocene miocene boundary and the middle miocene climate optimum we further describe and causally interpret the following features paleocene eocene warming trend the two step long term eocene cooling and the changes within the most recent interval miocene pliocene we review the scope and methods of constructing cenozoic stacks of benthic oxygen isotope records and present two new latitudinal stacks which capture besides global ice volume also bottom water temperatures at low less than 30 and high latitudes this review concludes with an identification of future directions for data collection statistical method development and climate modeling

patterns and controls of sediment production transfer and yield in the illgraben quantification of the volumes of sediment removed by rock slope failure and debris flows and identification of their coupling and controls are pertinent to understanding mountain basin sediment yield and landscape evolution this study captures a multi decadal period of hillslope erosion and channel change following an extreme rock avalanche in 1961 in the illgraben a catchment prone to debris flows in the swiss alps we analyzed photogrammetrically derived datasets of hillslope and channel erosion and deposition along with climatic and seismic variables for a 43 year period from 1963 to 2005 based on these analyses we identify and discuss 1 patterns of hillslope production channel transfer and catchment sediment yield 2 their dominant interactions with climatic and seismic variables and 3 the nature of hillslope channel coupling and implications for sediment yield and landscape evolution in this mountain basin our results show an increase in the mean hillslope erosion rate in the 1980s from 0 24 0 01 m yr 1 to 0 42 0 03 m yr 1 that coincided with a significant increase in air temperature and decrease in snow cover depth and duration which we presume led to an increase in the exposure of the slopes to thermal weathering processes the combination of highly fractured slopes close to the threshold angle for failure and multiple potential triggering mechanisms means that it is difficult to identify an individual control on slope failure on the other hand the rate of channel change was strongly related to variables influencing runoff a period of particularly high channel erosion rate of 0 74 0 02 m yr 1 1992 1998 coincided with an increase in the frequency and magnitude of intense rainfall events hillslope erosion exceeded channel erosion on average indicative of a downslope directed coupling relationship between hillslope and channel and demonstrating the first order control of rock slope failure on catchment sediment yield and landscape evolution

a combined study of radar facies lithofacies and three dimensional architecture of an alpine alluvial fan illgraben fan switzerland alluvial fans serve as useful archives that record the history of depositional and erosional processes in mountainous regions and thus can reveal the environmental controls that influenced their development economically they play an important role as groundwater reservoirs as well as host rocks for hydrocarbons in deeply buried systems the interpretation of these archives and the evaluation of their reservoir architecture however are problematic because marked heterogeneity in the distribution of sedimentary facies makes correlation difficult this problem is compounded because the accumulated sedimentary deposits of modern unconsolidated fan systems tend to be poorly exposed and few such systems have been the focus of investigation using high resolution subsurface analytical techniques to overcome this limitation of standard outcrop analogue studies a geophysical survey of an alpine alluvial fan was performed using ground penetrating radar to devise a scaled three dimensional subsurface model radar facies were classified and calibrated to lithofacies within a fan system that provided outcropping walls and these were used to derive a three dimensional model of the sedimentary architecture and identify evolutionary fan stages the illgraben fan in the swiss alps was selected as a case study and a network of ca 60 km sections of ground penetrating radar was surveyed seven radar facies types could be distinguished which were grouped into debris flow deposits and stream flow deposits assemblages of these radar facies types show three depositional units which are separated by continuous fan wide reflectors they were interpreted as palaeo surfaces corresponding to episodes of sediment starvation that affected the entire fan an overall upward decline in the proportion of debris flow deposits from ca 50 to 15 and a corresponding increase in stream flow deposits were identified the uppermost depositional unit is bounded at its base by a significant incision surface up to 700 m wide which was subsequently filled up mostly by stream flow deposits the pronounced palaeo surfaces and depositional trends suggest that allocyclic controls governed the evolution of the illgraben fan making this fan a valuable archive from which to reconstruct past sediment fluxes and environmental change in the alps the results of the integrated outcrop geophysical approach encourage similar future studies on fans to retrieve their depositional history as well as their potential reservoir properties

sedimentary aspects and paleoenvironmental evolution of a rift basin salta group cretaceous paleogene northwestern argentina the rift history of the salta basin is related to the evolution of the central andes and to the activity of the pacific margin owing to its geographic location sedimentation occurred from the neocomian to the paleogene with deposits reaching up to 5 000 m in thickness paleoenvironmental analysis reveals an evolutionary history controlled by tectonic and climatic changes isolated grabens characterized the early synrift stage differential subsidence provoked distinct environments in the southern and northern subbasins in the southern subbasins alluvial fan fluvial fan and lacustrine deposits prevail whilst in the northern subbasins eolian and fluvial environments dominate during the maastrichtian two major factors controlled the basin fill the decrease in tectonic subsidence and a relative sea level rise as recorded in south america an extensive and shallow atlantic marine ingression installed a carbonate system coincident with mainly humid conditions until the danian until the middle eocene the fluvial and lacustrine environmental evolution of the sag basin was controlled especially by the alternation of temperate with dry and humid periods paleontological records reflect these climatic changes and show their relationship to the sedimentation regime

experimental study of bedrock erosion by granular flows 1 field studies suggest that bedrock incision by granular flows may be the primary process cutting valleys in steep unglaciated landscapes an expression has been proposed for debris flow incision into bedrock which posits that erosion rate depends on stresses due to granular interactions at the snout of debris flows here we explore this idea by conducting laboratory experiments to test the hypothesis that bedrock erosion is related to grain collisional stresses which scale with shear rate and particle size we placed granular material in a 56 cm diameter rotating drum to explore the relationship between erosion of a synthetic bedrock sample and variables such as grain size shear rate water content and bed strength grain collisional stresses are estimated as the inertial stress using the product of the squares of particle size and vertical shear rate our uniform granular material consisted of 1 mm sand and quartzite river gravel with means of 4 6 or 10 mm in 67 experimental runs the eroded depth of the bed sample varied with inertial stresses in the granular flow to a power less than 1 0 and inversely with the bed strength the flows tended to slip on smooth boundaries resulting in higher erosion rates than no slip cases we found that lateral wall resistance generated shear across the channel producing two cells whose widths depended on wall roughness while the hypothesized inertial stress dependency is supported with these data wear mechanics needs to account for grain dynamics specifically at the snout and possibly to include lateral shear effects

tempo and scale of late paleocene and early eocene carbon isotope cycles implications for the origin of hyperthermals abstract the upper paleocene and lower eocene are marked by several prominent 1 carbon isotope 13c excursions cie that coincide with transient global warmings or thermal maxima including the paleocene eocene thermal maximum petm the cie which are recorded mainly in marine sedimentary sequences have also been identified in continental sequences occurred episodically and yet appear to be paced or triggered by orbital forcing to constrain the timing and scale of the cie relative to long term baseline variability we have constructed a 4 52 million year myr long high resolution 3 kyr bulk sediment carbon isotope record spanning the lower eocene to upper paleocene c25r c24n from a pelagic sediment section recovered at odp site 1262 in the southeast atlantic this section which was orbitally tuned utilizing high resolution core log physical property and geochemical records is the most stratigraphically complete upper paleocene to lower eocene sequence recovered to date time series analysis of the carbon isotope record along with a high resolution fe intensity record obtained by xrf core scanner reveal cyclicity with variance concentrated primarily in the precession 21 kyr and eccentricity bands 100 and 400 kyr throughout the upper paleocene lower eocene in general minima in 13c correspond with peaks in fe i e carbonate dissolution both of which appear to be in phase with maxima in eccentricity this covariance is consistent with excess oceanic uptake of isotopically depleted carbon resulting in lower carbonate saturation during periods of high eccentricity this relationship includes all late paleocene and early eocene cie confirming pacing by orbital forcing the lone exception is the petm which appears to be out of phase with the 400 kyr cycle though possibly in phase with the 100 kyr cycle reinforcing the notion that a mechanism other than orbital forcing and or an additional source of carbon is required to account for the occurrence and unusual scale of this event

characterizing the primary material sources and dominant erosional processes for post fire debris flow initiation in a headwater basin using multi temporal terrestrial laser scanning data abstract wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce hazardous debris flows relative to shallow landslides the primary sources of material and dominant erosional processes that contribute to post fire debris flow initiation are poorly constrained improving our understanding of how and where material is eroded from a watershed during a post fire debris flow requires 1 precise measurements of topographic change to calculate volumetric measurements of erosion and deposition and 2 the identification of relevant morphometrically defined process domains to spatially constrain these measurements of erosion and deposition in this study we combine the morphometric analysis of a steep small 0 01 km 2 headwater drainage basin with measurements of topographic change using high resolution 2 5 cm multi temporal terrestrial laser scanning data made before and after a post fire debris flow the results of the morphometric analysis are used to define four process domains hillslope divergent hillslope convergent transitional and channelized incision we determine that hillslope divergent and hillslope convergent process domains represent the primary sources of material over the period of analysis in the study basin from these results we conclude that raindrop impact induced erosion ravel surface wash and rilling are the primary erosional processes contributing to post fire debris flow initiation in the small steep headwater basin further work is needed to determine 1 how these results vary with increasing drainage basin size 2 how these data might scale upward for use with coarser resolution measurements of topography and 3 how these results change with evolving sediment supply conditions and vegetation recovery