experimental alluvial fans advances in understanding of fan dynamics and processes alluvial fans are depositional systems that develop because of a disparity between the upstream and downstream sediment transport capacity of a system usually at the base of mountain fronts as rivers emerge from the constrained mountain area onto the plain they are dynamic landforms that are prone to abrupt changes on a geomorphological decades to centuries time scale while also being long term deposition features that preserve sedimentary strata and are sensitive indictors of environmental change the complexity of interactions between catchment characteristics climate tectonics internal system feedbacks and environmental processes on field alluvial fans means that it is difficult to isolate individual variables in a field setting therefore the controlled conditions afforded by experimental models has provided a novel technique to overcome some of these complexities the use of experimental models of alluvial fans has a long history and these have been implemented over a range of different research areas utilising various experimental designs using this technique important advances have been made in determining the primary factors influencing fan slope understanding of avulsion dynamics identifying autogenic processes driving change on fan systems independent of any change in external conditions and the mechanics of flow and flood risk on alluvial fans to name a few however experiments cannot be carried out in isolation thus combining the findings from experimental alluvial fans with field research and numerical modelling is important and likewise using these techniques to inform experimental design if this can be achieved there is potential for future experimental developments to explore key alluvial fan issues such as stratigraphic preservation potential and simulating extra terrestrial fan systems

a stratigraphic framework for the preservation and shredding of environmental signals the stratigraphic record contains unique information about past landscapes and environmental change whether landscapes faithfully transmit signals of environmental change to stratigraphy is unknown because autogenic processes such as river avulsion can obscure signals prior to long term stratigraphic storage we develop a theoretical framework that predicts when a sediment flux signal will be transferred from the landscape to stratigraphy this threshold magnitude is a function of signal duration the magnitude is set by the maximum rate of autogenic volume change of the landscape which decreases with increasing time window physical delta experiments specifically designed to test our theory demonstrate that only sediment supply signals with a magnitude greater than the threshold are stored in stratigraphy supporting our theory this framework allows us to assess the fidelity of the stratigraphic record to archive past signals of environmental change and predict the short and long term impact of current anthropogenic forcing on landscapes

interpreting avulsion process from ancient alluvial sequences guadalope matarranya system northern spain and wasatch formation western colorado alluvial deposits of the guadalope matarranya system oligocene ebro basin spain and the wasatch formation eocene western colorado provide time integrated records of the process of river channel avulsion these sequences consist of isolated channel belt sandstones incised into and abruptly overlain by flood plain siltstones indicating deposition by avulsive river systems the geometry and distribution of channel incisions suggest that avulsion was not controlled by tectonics climate or base level changes but formed by autocyclic processes measurements from 221 channel fills in the guadalope matarranya system and 38 from the wasatch formation allow us to statistically characterize channel geometries we infer to be associated with establishment and abandonment of individual river avulsions paleoflow depths in both systems average 1 4 to 1 6 m aggradation height superelevation of channel margin levees are on average 0 6 and 1 1 times paleoflow depth in the guadalope matarranya and wasatch systems respectively these results are consistent with values from recently avulsed modern rivers and suggest that 1 flow depth is the appropriate parameter against which to scale the critical superelevation necessary for channel avulsion and 2 the increase in potential energy due to channel perching drives the lateral instability that is needed for avulsion to be successful numerous stacked channel fills indicate repeated reoccupation of the same site by avulsing channels these reoccupation channels indicate that inherited flood plain topography here abandoned channel forms was an important control on the arrival site of newly avulsed channels comparison of our results to others suggests two end member types of avulsion can take place incisional avulsion seen here is characterized by an early incision phase followed by infilling by migrating bar forms aggradational avulsion begins with aggradation followed in time by stream integration into a single downcutting channel we suggest that the type of avulsion is strongly influenced by whether or not the adjacent flood plain is well or poorly drained in both cases subsequent aggradation and channel perching increase the chances that some triggering event will lead to avulsion

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

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

transience and persistence in the depositional record of continental margins 1 continental shelves and coastal plains are large persistent depositional landforms which are stationary nonmigrating at their proximal ends and characterized by relatively steady long term growth in detail however their surface form and stratigraphic record is built of transient freely migrating landscape elements we derive the timescales of crossover from transient to persistent topographic forms using empirical scaling relations for mean sediment accumulation as a function of averaging time based upon tens of thousands of empirical measurements a stochastic noisy diffusion model with drift predicts all the gross features of the empirical data it satisfies first order goals of describing both the surface morphology and stratigraphic completeness of depositional systems the model crossover from noise dominated to drift dominated behavior corresponds to the empirical crossover from transport dominated autogenic transient behavior to accommodation dominated subsidence persistent behavior which begins at timescales of 102 103 years and is complete by scales of 104 105 years because the same long term scaling behavior emerges for off shelf environments it is not entirely explicable by steady subsidence fluctuations in sediment supply and routing probably have significant influence at short term transient scales the exponents of the scaling relations vary with environment particularly the prevalence of channeled sediment transport at very small scales modeling sediment transport as a diffusive process is inappropriate our results indicate that some of the timescales of interest for climate interpretation may fall within the transitional interval where neither accommodation nor transport processes are negligible and deconvolution is most challenging

signatures of climate vs sea level change within incised valley fill successions quaternary examples from the texas gulf coast abstract the passive margin texas gulf of mexico coastal plain consists of coalescing late pleistocene to holocene alluvial deltaic plains constructed by a series of medium to large fluvial systems alluvial deltaic plains consist of the pleistocene beaumont formation and post beaumont coastal plain incised valleys a variety of mapping outcrop core and geochronological data from the extrabasinal colorado river and the basin fringe trinity river show that beaumont and post beaumont strata consist of a series of coastal plain incised valley fills that represent 100 kyr climatic and glacio eustatic cycles valley fills contain a complex alluvial architecture falling stage to lowstand systems tracts consist of multiple laterally amalgamated sandy channelbelts that reflect deposition within a valley that was incised below highstand alluvial plains and extended across a subaerially exposed shelf the lower boundary to falling stage and lowstand units comprises a composite valley fill unconformity that is time transgressive in both cross and down valley directions coastal plain incised valleys began to fill with transgression and highstand and landward translation of the shoreline paleosols that define the top of falling stage and lowstand channelbelts were progressively onlapped and buried by heterolithic sandy channelbelt sandy and silty crevasse channel and splay and muddy floodbasin strata transgressive to highstand facies scale architecture reflects changes through time in dominant styles of avulsion and follows a predictable succession through different stages of valley filling complete valley filling promoted avulsion and the large scale relocation of valley axes before the next sea level fall such that successive 100 kyr valley fills show a distributary pattern basic elements within coastal plain valleys can be correlated with the record offshore where cross shelf valleys have been described from seismic data falling stage to lowstand channelbelts within coastal plain valleys were feeder systems for shelf phase and shelf margin deltas respectively and demonstrate that falling stage fluvial deposits are important valley fill components signatures of both upstream climate change vs downstream sea level controls are therefore interpreted to be present within incised valley fills signatures of climate change consist of the downstream continuity of major stratigraphic units and component facies which extends from the mixed bedrock alluvial valley of the eroding continental interior to the distal reaches wherever that may be at the time this continuity suggests the development of stratigraphic units and facies is strongly coupled to upstream controls on sediment supply and climate conditions within hinterland source regions signatures of sea level change are critical as well sea level fall below the elevation of highstand depositional shoreline breaks results in channel incision and extension across the newly emergent shelf which in turn results in partitioning of the 100 kyr coastal plain valleys moreover deposits and key surfaces can be traced from continental interiors to the coastal plain but there are downstream changes in geometric relations that correspond to the transition between the mixed bedrock alluvial valley and the coastal plain incised valley channel incision and extension during sea level fall and lowstand with channel shortening and delta backstepping during transgression controls the architecture of coastal plain and cross shelf incised valley fills

varying discharge controls on timescales of autogenic storage and release processes in fluvio deltaic environments tank experiments 1 changes in external forcing have traditionally been the main areas of interest in understanding sedimentary records while in most stratigraphic interpretation autogenic behavior has been thought of as a noise generator this study aims to investigate autogenic processes in a fluvio deltaic system under a range of discharge conditions and to show that autogenic processes generate distinct signatures rather than random noise a matrix of nine different experiments is presented here to systematically evaluate the effects of sediment and water discharge variations on the timescale of fluvial autogenic processes temporary sediment storage regularly occurs by backfilling of sediment in the fluvio deltaic channels followed by a period of strong channelization that releases the stored sediment these storage and release processes cycle along with changes in the fluvial slope and planform pattern of the flow here we propose that the autogenic behavior of deltaic progradation has a distinct timescale that is controlled by sediment and water discharges an increase in sediment discharge primarily reduces the autogenic timescale as higher sediment supply fills the channels faster in contrast the high sediment discharge causes a morphologic feedback by increasing the magnitude of fluvial slope change between the storage and release events and increasing the size of the temporary sediment storage termed the fluvial envelope this works against the sediment discharge control as the autogenic timescale is increased increasing the water discharge increases the autogenic timescale by improving the fluvial organization toward a strongly channelized system changes in autogenic timescale due to variations in the sediment and water discharges are nonlinear for different sediment to water discharge ratios as the ratio decreases the fluvial system is better organized and the timescale is more linearly related to the change in sediment discharge as the ratio increases deltas develop poorly organized fluvial systems and the associated timescales converge even with different sediment discharges the results presented here provide enhanced interpretation of sedimentary records by better decoupling of autogenic signatures from allogenic products developed across a wide range of discharge conditions

real and apparent changes in sediment deposition rates through time 1 field measurements show that estimated sediment deposition rate decreases as a power law function of the measurement interval this apparent decrease in sediment deposition has been attributed to completeness of the sedimentary record the effect arises because of incorporation of longer hiatuses in deposition as averaging time is increased we demonstrate that a heavy tailed distribution of periods of nondeposition hiatuses produces this phenomenon and that observed accumulation rate decreases as t 1 over multiple orders of magnitude where 0 1 is the parameter describing the tail of the distribution of quiescent period length by using continuous time random walks and limit theory we can estimate the actual average deposition rate from observations of the surface location over time if geologic and geometric constraints place an upper limit on the length of hiatuses then average accumulation rates approach a constant value at very long times our model suggests an alternative explanation for the apparent increase in global sediment accumulation rates over the last 5 million years

formation of mesosiderites by low velocity impacts as a natural consequence of planet formation mesosiderites are an enigmatic class of stony iron meteorites composed of roughly equal amounts of pyroxenitic and basaltic silicates and metallic iron nickel olivine is rare we suggest here that during the period of planet formation mesosiderites originated by the low velocity collisions of large metallic core fragments with the surface of a differentiated asteroid size body relative velocities of the asteroids native to this region were low 1 km s 1 because it was distant from massive protoplanets however a few differentiated asteroids were destroyed by high velocity collisions with interlopers perturbed by protoplanets into highly eccentric orbits these collisions reduced mantles and crusts to small silicate fragments but left cores in the form of large durable metal fragments mesosiderite like pyroxenite basalt metal mixtures were formed when large core fragments accreted at low velocities to the regolith of an intact asteroid the metal contents of other regolithic regions remained low most of the olivine in mesosiderite and howardite breccias we attribute to the mantles of the disrupted parent bodies the low 12 20 mg g 1 olivine contents indicate that the amount of debris accreted from disrupted asteroids was small relative to the volumes of the regoliths

morphodynamic modeling of fluvial channel fill and avulsion time scales during early holocene transgression as substantiated by the incised valley stratigraphy of the trinity river texas the trinity river system provides a natural laboratory for linking fluvial morphodynamics to stratigraphy produced by sea level rise because the sediments occupying the trinity incised valley are well constrained in terms of timing of deposition and facies distribution herein the trinity river is modeled for a range of base level rise rates avulsion thresholds and water discharges to explore the effects of backwater induced in channel sedimentation on channel avulsion the findings are compared to observed sediment facies to evaluate the capability of a morphodynamic model to reproduce sediment deposition patterns base level rise produces mobile locations of in channel sedimentation and deltaic channel avulsions for scenarios characteristic of early holocene sea level rise 4 3 mm yr 1 the trinity fluvial deltaic system progrades 13 m yr 1 followed by backstepping of 27 m yr 1 avulsion is reached at the position of maximum sediment deposition located 108 km upstream of the outlet after 3 548 model years based on sedimentation filling 30 of the channel under scenarios of greater base level rise avulsion is impeded because the channel fill threshold is never achieved accounting for partitioning of bed material sediment between the channel and floodplain influences the timing and location of avulsion over millennial time scales the time to avulsion is greatly increased sedimentation patterns within the valley modeled and measured indicate preference toward sandy bed material and the rates of deposition are substantiated by previous measurements although the results here are specific to the trinity river the analysis provides a framework that is adaptable to other lowland fluvial deltaic systems

complexity in a cellular model of river avulsion abstract we propose a new model of river avulsion that emphasizes simplicity self organization and unprogrammed behavior rather than detailed simulation the model runs on a fixed cellular grid and tracks two elevations in each cell a high elevation representing the channel levee top and a low one representing the channel bottom the channel aggrades in place until a superelevation threshold for avulsion is met after an avulsion is triggered a new flow path is selected by steepest descent based on the low values of elevation flow path depends sensitively on floodplain topography particularly the presence of former abandoned channels several behavioral characteristics emerge consistently from this simple model 1 a tendency of the active flow to switch among a small number of channel paths which we term the active channel set over extended periods leading to clustering and formation of multistory sand bodies in the resulting deposits 2 a tendency for avulsed channels to return to their previous paths so that new channel length tends to be generated in relatively short segments and 3 avulsion related sediment storage and release leading to pulsed sediment output even for constant input each of these behaviors is consistent with observations from depositional river systems a single valued threshold produces a wide variety of avulsion sizes and styles larger nodal avulsions are rarer because pre existing floodplain topography acts to steer flow back to the active channel channel stacking pattern is very sensitive to floodplain deposition this work highlights the need to develop models of floodplain evolution at large time and space scales to complement the improving models of river channel evolution

conditions for branching in depositional rivers it is often taken for granted that rivers organize transport into a single active channel in some net depositional environments however flow of water and sediment is distributed in several stable channels such branching rivers may be confined in valleys anabranching or anastomosed or unconfined on deltas distributaries and their existence confronts us with the very basic question of what governs the spatial organization of channel patterns in sedimentary landscapes current models for equilibrium channel morphology cannot predict the occurrence of branching rivers because they do not consider dynamical processes such as avulsion i e the rapid abandonment of a channel in favor of a new path at lower elevation the requisite conditions for avulsion have been the subject of ongoing debate here we resolve the conditions leading to channel avulsion and show that branching rivers occur when avulsion is the dominant mechanism of lateral channel motion a compilation of field and laboratory data demonstrates that avulsion frequency scales with the time required for sedimentation on channel beds to produce a deposit equal to one channel depth from the relative rates of bank erosion and channel sedimentation we derive a dimensionless mobility number that accurately predicts the conditions under which anabranching and distributary channels occur results may be directly applied to modeling landscape evolution over human and geologic time scales and for inverting formative environmental conditions from channel deposits on earth and other planetary surfaces

synthetic stratigraphy with a stochastic diffusion model of fluvial sedimentation abstract models of stratigraphic completeness and bed formation in fluvial depositional environments have most often assumed that successive depositional and erosional events deposit or erode amounts of sediment independently this results in a random walk model for the total amount of deposited sediment locally as a function of time we consider an extension of the random walk model of sedimentation in an alluvial plain in which deposition or erosion is concentrated in randomly avulsing channels and sediment transport is modeled by the diffusion equation culling s model in contrast to the random walk model this model results in an anticorrelated sequence locally as a function of time i e after an area has aggraded it has a higher elevation and a lower rate of future aggradation in a p evious paper we analyzed the topography generated by the model and argued that porosity variations could be associated with topographic variations the power spectrum s the square of the coefficients in a fourier series of one dimensional transects of topography and porosity horizontally and vertically in this model have a power law dependence on wave number k s k k s with values of s close to those observed in this paper we show that the model deposits sediment with a rate depending on time interval as a power law with exponent 3 4 more consistent with observations than the random walk model the model produces an exponential bed thickness distribution with a skew depen ent on the sedimentation rate of the basin in accordance with observations we also examine the persistence in the series of bed thicknesses as a function of depth for the stochastic diffusion model of sedimentation no persistence is observed if the model fully characterizes the autocyclic dynamics in fluvial sedimentary basins the lack of persistence in the synthetic bed sequences suggests that observed persistence and cyclicity in real bed thickness sequences must be the result of allocyclic processes

predicting delta avulsions implications for coastal wetland restoration river deltas create new wetlands through a continuous cycle of delta lobe extension avulsion and abandonment but the mechanics and timing of this cycle are poorly understood here we use physical experiments to quantitatively define one type of cycle for river dominated deltas the cycle begins as a distributary channel and its river mouth bar prograde basinward eventually the mouth bar reaches a critical size and stops prograding the stagnated mouth bar triggers a wave of bed aggradation that moves upstream and increases overbank flows and bed shear stresses on the levees an avulsion occurs as a time dependent failure of the levee where the largest average bed shear stress has been applied for the longest time r 2 0 93 these results provide a guide for predicting the growth of intradelta lobes which can be used to engineer the creation of new wetlands within the delta channel network and improve stratigraphic models of deltas

significance of channel belt clustering in alluvial basins the distribution of channel deposits in alluvial basins is commonly used to interpret past changes in climate tectonics and sea level here we present preliminary evidence that longtime scale 10 3 10 5 yr self organization in fl uvial systems may generate structured stratigraphic patterns spontaneously in the absence of or independent from changing basin boundary conditions a physical experiment and an ancient alluvial succession ferris formation latest cretaceous paleogene south central wyoming both show stratigraphy where clusters of many closely spaced channel deposits are separated from each other by extensive intervals of overbank mudstones analysis using spatial point process methods shows that channel deposits in both basins are statistically clustered over intermediate basin length scales in the experiment external controls base level subsidence rate and sediment water supplies were not varied and therefore not factors in cluster formation likewise the ancient system lacks stratigraphic and sedimentologic evidence of external controls on channel clustering we propose that channel clusters as seen in this study refl ect a scale of flself organization that is not usually recognized in ancient deposits this type of internally generated stratigraphy should be considered when reconstructing tectonic climate and sea level changes from

geomorphology and sequence stratigraphy due to slow and rapid base level changes in an experimental subsiding basin xes 96 1 subsidence is a major factor in the accumulation and architecture of natural basin fills a recently built experimental facility experimental earthscape facility xes at st anthony falls laboratory of the university of minnesota incorporates for the first time a flexible subsiding floor in its design thus the experimental basin can model erosion and deposition associated with independent variations in sediment supply absolute base level change and rates and geometries of subsidence the results of the first experiment in a prototype basin 1 1 6 0 8 m are described here wherein the stratigraphic development associated with first slow and then rapid base level cycles in a basin that has a sag geometry has been analyzed a videotape of the experiment and subsequent serial slicing of the dried strata in the basin allow interpretation of the sequence development under conditions of precisely known changes of absolute base level subsidence and sedimentation relative base level changes which strongly varied in the basin owing to the sag geometry of subsidence seem to exert primary control on sedimentary patterns although autocyclic changes were also important style of sequence boundaries differed between slow and fast base level falls during the slow base level fall an incised valley developed once the shoreline prograded out of the zone of maximum subsidence suggesting that incision at the shoreline may be very sensitive to changes in relative base level once started however the valley quickly widened by knickpoint retreat into a broad low relief erosion surface that stretched across the entire basin as erosion took place at the knickpoint deposition occurred immediately downflow so both the knickpoint and the upstream limit of deposition migrated landward together producing a strong time transgressive erosion and onlap sequence the stratigraphic begin page 818 record of this sequence boundary is a single yet very subtle widespread unconformity that becomes conformable downstream which is difficult to trace in stratigraphic cross section in contrast the incised valley that formed during the rapid base level fall was relatively narrow deep and lengthened over time as deposits at the mouth of the valley were gradually exposed and incised through wholesale backfilling of the incised valley did not begin until the rapid base level rise started as a result the rapid base level change produced a more easily recognized incised valley in the stratigraphic record than did the slow base level change potential reservoir development within the strata is evaluated by means of a gray scale proxy for porosity four distinctive zones of enhanced reservoir quality occurred in the basin the most proximal part of the basin the upper part of growth fault bounded sedimentary wedges deep water forced regressive systems tract composed of grainflow deposits and transgressive systems tract formed during the rapid base level rise this distribution of relatively porous units suggests that for a variety of reasons rapid sea level cycles may produce the best reservoir units

influence of water and sediment supply on the long term evolution of alluvial fans and deltas statistical characterization of basin filling sedimentation patterns 1 the temporal and spatial variability of sedimentation resulting from sediment storage and release and the lateral mobility of sediment transporting flows imparts fundamental patterns into the stratigraphic record recent studies show that paleoenvironmental allogenic signals preserved in stratigraphy may be contaminated by internally generated autogenic sedimentation patterns however it is unclear how the magnitude of autogenic dynamics is related to allogenic forcings utilizing statistical methods we quantify basin filling trends in three laboratory experiments where input water and sediment flux were varied we use the compensation index and compensation time scale to estimate the strength of compensation defined here as the tendency to fill topographic lows faster than would result from random deposit stacking and to estimate the time scales over which autogenic processes operate in the experiments topography of channelized deltas formed by noncohesive sediment was monitored in a basin experiencing temporally and spatially uniform relative subsidence each experiment resulted in construction of a stratigraphic package in excess of 25 channel depths thick we find that compensation strength in the experiments is not influenced by absolute magnitudes of water and sediment flux but does increase as a function of the ratio of water to sediment flux a compensation time scale defined as the maximum depth of a system s channels divided by the long term deposition rate accurately defines the maximum time scale at which autogenic dynamics occur in all experiments when applied to field scale systems we predict that autogenic dynamics occur out to time scales between 5 and 150 kyr

scale dependent compensational stacking an estimate of autogenic time scales in channelized sedimentary deposits recent studies show that paleoenvironmental allogenic signals preserved in the stratigraphic record may be contaminated or overprinted by internally generated autogenic sedimentation this is problematic but it is unclear over what temporal and spatial scales autogenic patterns are most prevalent we propose that scale breaks in basin fi lling trends can be used to identify the transition between allogenic and autogenic stratigraphy using data from numerical and physical experiments and an ancient outcrop we explore how compensation the tendency for sediment transport systems to preferentially fi ll topographic lows varies with stratigraphic scale object based models demonstrate the temporal scales at which stratigraphy changes from being partially infl uenced by autogenic processes to being completely determined by allo genic forcings and suggest that this transition occurs at a time scale set by the maximum scale of surface roughness in a transport system divided by the long term aggradation rate this hypothesis is validated in a physical experiment where delta topography was monitored along fl ow perpendicular transects at a high temporal resolution relative to channel kine matics the strength of compensation in the experiment changes at the predicted time scale where the maxi mum surface roughness is equal to the depth of the experimental channels above this compensation time scale deposits stack purely compensationally but below this time scale deposits stack somewhere between randomly and deterministically similar scale dependent stacking is also observed in the ferris formation cretaceous paleogene hanna basin wyoming united states this study demonstrates that scale dependent compensational stack ing may be useful for isolating allogenic and autogenic stratigraphy in sedimentary basins

influence of water and sediment supply on the stratigraphic record of alluvial fans and deltas process controls on stratigraphic completeness 1 stratigraphy contains the most complete record of information necessary to quantitatively reconstruct paleolandscape dynamics but this record contains significant gaps over a range of time and space scales these gaps result from stasis on geomorphic surfaces and erosional events that remove previously deposited sediment building on earlier statistical studies we examine stratigraphic completeness in three laboratory experiments where the topography of aggrading deltas was monitored at high temporal and spatial scales the three experiments cover unique combinations in the absolute magnitudes of sediment and water discharge in addition to generation of accommodation space through base level rise this analysis centers on three time scales 1 the time at which a record is discretized t 2 the time necessary to build a deposit with mean thickness equivalent to the maximum roughness on a surface tc and 3 the time necessary for channelized flow to migrate over all locations in a basin tch these time scales incorporate information pertaining to the time variant topography of actively changing surfaces kinematics by which the surfaces are changing and net deposition rate we find that stratigraphic completeness increases as a function of t tc but decreases as a function of tc tch over the parameter space covered in the experiments our results suggest that environmental signals disconnected from a sediment routing system are best preserved in systems with low tc values nondimensionalizing t by tc however shows that preservation of information characterizing system morphodynamics is best preserved in stratigraphy constructed by systems with low water to sediment flux ratios

a revised chronology for mississippi river subdeltas radiocarbon measurements by accelerator mass spectrometry relating to three of the four late holocene mississippi river subdeltas yielded consistent results and were found to differ by up to 2000 carbon 14 years from previously inferred ages these geological dataare in agreement with archaeological carbon 14 data and stratigraphic ages based on ceramic seriation and were used to develop a revised chronologic framework which has implications for prehistoric human settlement patterns coastal evolution and wetland loss and sequence stratigraphic interpretations

how much subsidence is enough to change the morphology of river deltas understanding the effect of subsidence on fluviodeltaic morphology is important not only to maintain sustainable coastal cities and habitats but also to interpret the information contained in the stratigraphic record while tectonic steering in alluvial environments has been investigated similar studies in fluviodeltaic environments are limited to physical experiments and field observations we perform numerical experiments with a parcel based cellular model to analyze the deltaic surface and subsurface responses to regional subsidence we quantify model results using robust metrics and show that while sediment partitioning and shoreline pattern vary gradually with increasing subsidence rate channel mobility and stratigraphic connectivity of channel deposits show a threshold transition conditions for this transition are captured with a dimensionless filling index defined as the ratio between the rates of accommodation creation and sediment supply a channel locking mechanism activates when exceeds 0 6 and is responsible for the threshold transition

integrated stratigraphy and 40ar 39ar chronology of early middle miocene sediments from dsdp leg 42a site 372 western mediterranean abstract an integrated magneto biostratigraphic framework is presented for middle miocene sediments of dsdp site 372 located in the western mediterranean detailed biostratigraphic analysis shows a nearly complete sequence of early middle miocene calcareous plankton bioevents in the mediterranean including the lco last common occurrence of the nannofossil sphenolithus heteromorphus which has been astronomically dated in the ras il pellegrin rip section on malta island abels h a hilgen f j krijgsman w kruk r w raffi i turco e zachariasse w j 2005 long period orbital control on middle miocene global cooling integrated stratigraphy and astronomical tuning of the blue clay formation on malta paleoceanography 20 pa4012 doi 10 1029 2004pa001129 11 pp thermal demagnetization of discrete samples revealed a characteristic low temperature component with dual polarities despite a weak paleomagnetic signal the resultant magnetostratigraphic record combined with the calcareous plankton biostratigraphy is straightforwardly correlated to the geomagnetic polarity time scale ck95 of cande and kent cande s c kent d v 1995 revised calibration of the geomagnetic polarity time scale for the late cretaceous and cenozoic j geophys res 100 6093 6095 and the astronomical tuned neogene time scale atnts04 of lourens et al lourens l j hilgen f j laskar j shackleton n j wilson d 2004 the neogene period in gradstein f m ogg j g smith a g eds a geologic time scale cambridge univ press pp 409 440 the subchrons recorded in site 372 succession range from c5br up to c5aar to confirm the magnetostratigraphic calibration 40ar 39ar dating was performed on feldspar of two volcanic ash layers the radio isotopic dating indicates a younger age for these two ash layers compared to the magnetostratigraphic calibrated ages according to the ck95 and atnts04 age models however if the astronomically calibrated age of 28 21 0 04 ma is used for the fish canyon standard fcs the age for the older ash layer exactly matches its atnts04 age ages for bioevents were calculated assuming constant sedimentation rates between magnetostratigraphic age tie points the s heteromorphus lco has an age of 13 54 ma and 13 63 ma according to ck95 and atnts04 respectively which is consistent with the astronomical tuned age of 13 65 ma determined at rip section abels h a hilgen f j krijgsman w kruk r w raffi i turco e zachariasse w j 2005 long period orbital control on middle miocene global cooling integrated stratigraphy and astronomical tuning of the blue clay formation on malta paleoceanography 20 pa4012 doi 10 1029 2004pa001129 11 pp we therefore conclude that the magnetostratigraphic calibration of dsdp site 372 is correct and that for the time being this site can be considered as a reference section for the early middle miocene of the mediterranean region

astronomical climate control on paleosol stacking patterns in the upper paleocene lower eocene willwood formation bighorn basin wyoming the willwood formation of the bighorn basin wyoming usa is a thick succession of upper paleocene and lower eocene fluvial floodplain sandstones and mudstones reddish paleosols formed on the floodplain mudstones alternate rhythmically on various scales with heterolithic intervals of small channel sandstones and mudstones showing weak pedogenesis spectral analysis of redness in the willwood successions at polecat bench and red butte reveals significant spectral peaks corresponding to cycle thicknesses of 8 and 3 m the 8 m cycle reflects distinct clusters of 3 5 paleosols age constraints show that the period of this cycle closely matches the 21 k y climatic precession cycle the 3 m cycle corresponds to individual paleosols with a period of 7 8 k y this period is similar to millennial scale sub milankovitch cycles found in marine and lacustrine successions of pliocene pleistocene age precession and millennial scale climate variations probably affected paleosol development through cyclic changes from predominantly overbank to predominantly channel avulsion deposition with the latter periodically halting soil formation because of high sediment accumulation a new age model was developed for the paleocene eocene carbon isotope excursion cie at polecat bench based on the precessional origin of paleosol clusters the main body of the cie spans 5 5 precession cycles or 115 k y and the recovery tail of the cie spans 2 precession cycles or 42 k y this outcome is consistent with and independently confirms recent estimates of cie duration based on deep sea cores

mass balance effects in depositional systems abstract net deposition is necessarily accompanied by overall loss of sediment mass from the transport system on long time scales the deposition compensates for subsidence and creates the stratigraphic record although its spatial pattern changes and it can be locally stopped or reversed depositional mass loss is a fundamental driving influence on the morphology and behavior of depositional systems mass extraction to deposition leads directly to facies changes as sediment flux declines indirectly it usually leads to down channel sediment fining as deposition preferentially removes coarser particles laboratory experiments illustrate the effects of systematic mass extraction on fluvial channel stacking and deposit grain size and show how a mass balance framework allows consistent comparison of facies despite major shifts in depocenter location mass balance analysis of experimental fluvial and turbidite systems and a turbidite mini basin from the gulf of mexico show a change from channel dominated to lobe dominated deposits at about 80 total mass extraction experimental and field studies also show a close connection between rate of mass loss and rate of downstream grain size fining as predicted by a mechanistic theory based on mass balance these are first steps towards a framework for quantitative basin analysis based on mass extraction a mass balance framework allows for consistent quantitative comparison across basins of varying scale and shape mass balance frameworks can account for overall and or generic mass balance effects and help separate them from local effects one way to use such generalized models effectively is to view the results as reference cases of down transport change resulting from the basic interplay of spatial mass extraction pattern and sediment supply where such reference cases do not provide detailed predictions of specific field cases they can still provide a baseline to separate local case specific features from generic system behavior the approach is analogous to the way the geoid serves as a reference case against which to measure gravity anomalies

an experimental investigation of autogenic behaviour during alluvial fan evolution the findings from a series of laboratory experiments designed to examine the role of autogenic process form interactions as controls on alluvial fan evolution are presented the experimental approach follows the similarity of processes concept and is therefore not scaled to a real world prototype the experiments were conducted in the university of exeter sediment research facility using a 3 3 m fixed bed experimental table with controlled sediment and water supply fed to the fan apex and evacuation of all sediment that passes the distal boundary the evolution of the fan was recorded using high resolution time lapse overhead photography to permit analysis of fan topography flow patterns channel migration and avulsion on the fan surface over the course of the experimental run the qualitative observations from three experimental scenarios are discussed and evaluated in the context of current understanding of alluvial fan evolution these demonstrate that in the absence of any change in the extrinsic variables there is an autogenic transition from sheetflow to channelised flow as the experimental fans evolve this is consistent with theory that predicts this change in response to a decline in aggradation rate through time

temporal significance of sequence boundaries abstract this paper analyses the temporal significance of stratigraphic surfaces bounding the marine portions of the depositional sequence genetic stratigraphic sequence and transgressive regressive sequence these bounding surfaces known as the correlative conformity c c maximum flooding surface mfs and conformable transgressive surface cts respectively may either be defined on the basis of stratal stacking patterns which we call type a surfaces or on the basis of water depth changes and relative sea level changes which we call type b surfaces the type a mfs and cts are time lines in a depositional dip section corresponding to the turnaround points from shoreline transgression to regression and vice versa they separate prograding coarsening upward from retrograding fining upward geometries with a timing determined by the interplay between the rates of sedimentation and relative sea level rise in the shoreline area the timing of type a mfs and cts is not affected by the offshore variations in sedimentation and subsidence rates but it is only controlled by the shoreline movements and the associated facies shifts the type a c c separates rapidly prograding and offlapping forced regressive strata from the overlying lower rate prograding and aggrading normal regressive strata this surface is diachronous younger basinward with the rate of offshore sediment transport the timing of the type a c c in the shoreline area corresponds to the end of relative sea level fall but it develops under relative sea level rise conditions offshore the timing of the type b mfs and cts depends on the offshore variations in the sedimentation and subsidence rates these surfaces defined on the basis of bathymetric changes become younger and older seaward respectively tending to merge together offshore the type b c c marks the end of relative sea level fall in any point along a depositional dip section it is diachronous older basinward as its timing depends on the offshore variations in subsidence rates the diachroneity of type b surfaces reaches a quarter of the period of the highest frequency variable whichever that is among the eustasy tectonics or sedimentation controls types a and b surfaces merge together in the shoreline area but they become temporally divergent offshore deepening upward and shallowing upward facies should not be confused with transgressive and regressive systems tracts the latter are strictly controlled by the shoreline movements which determine the direction of facies shifts and the stratal stacking patterns

autogenic sedimentation in clastic stratigraphy internally generated or autogenic terrestrial and marine sediment transport dynamics can produce depositional patterns similar to those associated with climatic tectonic or sea level changes a central challenge in accurately interpreting the sedimentary archive is determining what scales and types of deposits reflect autogenic controls on sedimentation in different environments autogenic sediment transport dynamics commonly result from intermittent sediment storage in transient landforms which produces episodic spatially discontinuous sedimentation across a basin the transition from localized variable sedimentation to even basin wide sedimentation marks the shift from stochastic landscape dynamics to deterministic deposition responding to the long term balance between sediment supply and the creation of space to accommodate sediment this threshold can be measured in a wide variety of stratigraphic successions and has important bearing on whether climatic tectonic or sea level signals can be

the 2011 tohoku oki tsunami three years on abstract the 2011 tohoku oki tsunami that devastated the pacific coast of tohoku japan was a turning point for modern research as a result of this event it was recognized that paleotsunami research is vital to help understand the size and recurrence interval of low frequency large tsunamis this paper reviews the progress of geological research on the 2011 tohoku oki tsunami and summarizes new questions that are arising out of this work for example recent work suggests that the landward extent and thickness of the sandy deposit as well as the presence or absence of marine microfossils in the sediment are most likely to be mainly controlled by the initial wave properties sediment source offshore bathymetry and onshore topography this in turn implies that there are certain relationships between the characteristics of a tsunami deposit and the wave properties and it may be possible to reconstruct the latter from the deposits offshore tsunami deposits related to the 2011 tohoku oki tsunami have also been well described this recent research indicates that sedimentation and erosion in inner bay and open ocean 20 m water depth locations can be in the order of several meters suggesting that the tsunami shear force was strong in the nearshore zone on the other hand sandy to muddy deposits a few centimeters thick were observed at about 100 to 6000 m water depth it is likely that the tsunami resulted in resuspension of sea bottom sediments and that suspended material flowed downslope as a turbidity current or suspended flow although many authors recognize the possibility that strong earthquake groundshaking might have also generated turbidity currents studies of the 2011 tohoku oki event have led researchers back to two of the fundamental issues of tsunami geology understanding the linkage between onshore and offshore sedimentation and erosion and establishing identification criteria for tsunami deposits moreover though beyond the issue of simple tsunami geology it is important for all researchers to communicate with governments and the general public in order to reduce future casualties by using risk assessments based on our understanding of infrequent large tsunamis

long period cyclic sedimentation with constant tectonic forcing in an experimental relay ramp it is widely believed that cyclic sedimentation in active tectonic basins is caused by external forcing such as sea level cycles episodic tectonic events or variation in sediment supply due to climate change here we present a case of cyclic sedimentation in an experiment subject to constant fault slip rate and sediment discharge with no base level fluctuation the experiment was designed to study sedimentation in a simplified extensional relay ramp system reorganization of the fluvial channel network in a cyclic manner caused local variation in sediment supply to the hanging wall basin where subsidence was maximized and resulted in autogenic appearance and disappearance of a lake associated with 90 rotation of paleocurrent direction and delta formation comparing an early phase of the experiment using no external forcing i e no tectonic movement or base level change with the following main phase of the experiment i e including subsidence in an extensional relay ramp pattern shows that the characteristic time scale for channel mobility was five times longer during the phase with subsidence than during the previous phase without subsidence active fault slip imposed a new longer time scale for autogenic dynamics by establishing a linked tectonic sedimentation system scaling the experimental results to field length and time scales suggests that comparable autogenic cycles would produce 10 20 m thick strata on time scales of 105 yr comparable to observed cases attributed to allogenic effects

quantitative models of sedimentary basin filling summary quantitative modelling of the filling of sedimentary basins was begun in earnest in the 1960s dozens of themes and variations have been proposed since then and have yielded an abundance of idealized stratigraphic patterns as functions of both imposed changes and basin properties post plate tectonic modelling began with rigid lid models which show the stratigraphic signature of subsidence variation this work introduced the connection between stratigraphy and the rheology of the lithosphere rigid lid models are the simplest type of geometric model in which the sediment surface is assigned prescribed geometries usually corresponding to different depositional environments these can reproduce many aspects of overall stratal geometry but are formally restricted to relatively long timescales for which quasi steady surface topography can be assumed so called dynamic models attempt to represent the morphodynamics of the sediment surface by abstracting and averaging short term transport processes most of the dynamic models proposed to date can be seen as special cases of a single general morpho dynamic equation the most important result of the first wave of quantitative basin filling models is that even relatively simple models can produce reasonable stratal patterns we now have a wide array of tools for exploring scenarios searching for general behaviours and effects and making initial quantitative predictions we have also learned that basin response to external forcing as recorded in stratigraphy can be as sensitive to the characteristics of the basin as to the forcing the main brake on the development of basin modelling is not computing power but lack of methods and data for testing the models we have already developed physical experiments which are only just beginning are one means of doing this experimental stratigraphy is a bridge to quantitative field tests which will require collaboration among academic researchers from a wide range of areas and between academia and industry on projects of greater scale and degree of integration than we have seen so far the advancement of quantitative sedimentary geology will also require significant changes in the way the subject is taught at all levels

sequence stratigraphy of experimental strata under known conditions of differential subsidence and variable base level sequence stratigraphy has been applied from reservoir to continental scales providing a scale independent model for predicting the spatial arrangement of depositional elements we examine experimental strata deposited in the experimental earthscape facility at st anthony falls laboratory focusing on stratigraphic surfaces defined by discordant contact geometries surfaces analogous to those delineated in the original work on seismic sequence stratigraphy in this controlled setting we directly evaluate critical sequence stratigraphic issues such as stratigraphic horizon development and time significance as well as the internal geometry and migration of the bounded strata against the known boundary conditions and depositional history four key stratigraphic disconformities defined by marine downlap marine onlap fluvial erosion and fluvial onlap are mapped and vary greatly in their relative degree of time transgression marine onlap and downlap contacts closely parallel topographic surfaces time surfaces and prior to burial approximate the instantaneous offshore topography these stratal bounding surfaces are also robust stratigraphic signals of relative base level fall and rise respectively marine onlap surfaces are of special interest they tend to be the best preserved discordance where widespread allogenic based onlap surfaces subdivide otherwise amalgamated depositional cycles amidst cryptic stacks of marine foresets however local autogenic based marine onlap discordances are present throughout the fill a critical distinguishing feature of allogenic onlap is the greater lateral persistence of the discordance surfaces defined by subaerial erosional truncation and fluvial onlap do not have geomorphic equivalence because channel processes continually modify the surface as the stratigraphic horizons are forming hence they are strongly time transgressive last the stacking arrangement of the preserved bounded strata is found to be a good time averaged representation of the mass balance history

punctuated sand transport in the lowermost mississippi river 1 measurements of sand flux and water flow in the mississippi river are presented for a portion of the system 35 50 km upstream from the head of its subaerial delta these data are used to provide insight into how nonuniform flow conditions present in the lower reaches of large alluvial rivers affect the timing and magnitude of sand transport near the river outlet field surveys during both low and high water discharge include 1 sequential digital bathymetric maps defining mobile river bottom topography which were used to estimate bed material flux 2 multiple water velocity profiles and 3 multiple suspended sediment profiles collected using a point integrated sampler these data show that total sand transport increases by two orders of magnitude over the measured range in water discharge 11 300 to 38 400 m3 s 1 during low water discharge no sand is measured in suspension and sand discharge via bed form migration is minimal during high water discharge 54 of the sand discharge is measured in suspension while 46 of the sand discharge is part of bed form migration the component of boundary shear stress associated with moving this sediment is estimated using a set of established sediment transport algorithms and values for the total boundary shear stress are predicted by fitting logarithmic velocity functions to the measured profiles the estimates of boundary shear stress using measurements of suspended sand transport bed form transport and downstream oriented velocity profiles are internally consistent moreover the analyses show that boundary shear stress increases by nearly 10 fold over the measured water discharge range we show how this increase in shear stress is consistent with backwater flow arising where the river approaches its outlet the hydrodynamic properties of backwater flow affect the timing and magnitude of sand flux and produce punctuated sand transport through the lowermost mississippi river our field data are used to evaluate the influence of this sand transport style on development of the mixed bedrock alluvial channel for the lowermost mississippi river

the polymict eucrites the polymict eucrites are a suite of about 14 polymict achondritic meteorites that contain at least 90 vol of eucritic material and are found both in antarctica and elsewhere they are part of a continuum of polymict breccias that includes howardites and polymict diogenites rare gas data suggest that some are gas rich regolith breccias the clasts contained in polymict eucrites sample a variety of lithologies from their parent body and include eucritic clasts alkali enriched eucrites pyroxene cumulate eucrites two pyroxene mafic rocks possibly feldspar cumulate eucrites diogenites fayalitic lithologies and a variety of other mineral clasts the eucritic clasts are probably samples of near surface lithologies on the parent body but the presence of two pyroxene mafic rocks is considered to be evidence of magmatic activity at pressures in excess of 1 kbar in the parent body partial melt models may explain some of the diversity among the clasts but cumulus processes are believed to have been important if pressures greater than 1 kbar are confirmed then the basaltic achondrite parent body bap must have a diameter in excess of 200 km the variety of lithologies suggests that not all basaltic achondrites are samples of igneous rocks formed by single stage melting of a chondritic asteroid but are instead samples of an evolved and diverse crust produced by serial magmatism

causes of river avulsion insights from the late holocene avulsion history of the mississippi river u s a abstract the emphasis on gradient advantages in studies of avulsion is misleading while gradient advantages are necessary for an avulsion to occur the late holocene avulsion history of the mississippi river in louisiana suggests that factors such as substrate composition and floodplain channel distributions are more important cross valley to down valley slope ratios of the modern floodplain range from 16 to 110 and are typically 30 the slope ratio is 35 at the location of the mississippi atchafalaya diversion old river yet slope ratios are 83 to 110 immediately upvalley of old river all values of mississippi river floodplain slope ratios are significantly larger than values of avulsion threshold calculated by numerical models shallow floodplain cores 14c dating of organic remains and geologic mapping show that the mississippi river has avulsed only four times over the past 5 ky in the southern lower mississippi valley lmv gradient advantages are widespread yet avulsions are rare these observations indicate that factors other than gradient advantage control mississippi river avulsion several examples of mississippi and red river avulsion by channel reoccupation support the idea that channel distributions and substrate compositions are primary influences on avulsion incipient mississippi river avulsion and development of the atchafalaya river involved reoccupation of abandoned mississippi river channels and a red river crevasse splay complex the modern atchafalaya river also incises buried mississippi river channel belt sands abandoned channel belts and crevasse splay complexes consist of sandy substrates that facilitate scour and the development of channels capable of capturing the mississippi river abandoned channels provide ready made conduits for mississippi river flow that can efficiently develop into avulsive channels multi storied sheet sandstones in ancient fluvial deposits may provide additional support for the idea that erodible substrates and floodplain channel distributions are critical influences on avulsion these features record episodic reoccupation of channel belts which at least in some cases may simply reflect successive avulsions rather than major changes in aggradation rate or extrabasinal factors such as climate

climate driven unsteady denudation and sediment flux in a high relief unglaciated catchment fan using 26al and 10be panamint valley california abstract environmental changes within erosional catchments of sediment routing systems are predicted to modulate sediment transfer dynamics however empirical and numerical models that predict such phenomena are difficult to test in natural systems over multi millennial timescales tectonic boundary conditions and climate history in the panamint range california are relatively well constrained by existing low temperature thermochronology and regional multi proxy paleoclimate studies respectively catchment fan systems present there minimize sediment storage and recycling offering an excellent natural laboratory to test models of climate sedimentary dynamics we used stratigraphic characterization and cosmogenic radionuclides crns 26al and 10be in the pleasant canyon complex pcc a linked catchment fan system to examine the effects of pleistocene high magnitude high frequency climate change on crn derived denudation rates and sediment flux in a high relief unglaciated catchment fan system calculated 26al 10be burial ages from 13 samples collected in an 180 m thick outcropping stratigraphic succession range from ca 1 55 0 22 ma in basal strata to ca 0 36 0 18 0 52 0 20 ma within the uppermost part of the succession the mean long term crn derived paleodenudation rate 36 8 mm kyr 1 is higher than the modern rate of 24 0 6 mm kyr from pleasant canyon and paleodenudation rates during the middle pleistocene display some high frequency variability in the high end up to 54 10 mm kyr the highest crn derived denudation rates are associated with stratigraphic evidence for increased precipitation during glacial pluvial events after the middle pleistocene transition post ca 0 75 ma suggesting 100 kyr milankovitch periodicity could drive the observed variability we investigated the potential for non equilibrium sedimentary processes i e increased landslides or sediment storage recycling to influence apparent paleodenudation rates end member mixing models suggest that a mixture of 50 low crn concentration sediment from landslides is required to produce the largest observed increase in paleodenudation rate the overall pattern of crn derived burial ages paleodenudation rates and stratigraphic facies suggests milankovitch timescale climate transitions drive variability in catchment denudation rates and sediment flux or alternatively that climate transitions affect sedimentary process regimes that result in measurable variability of crn concentrations in unglaciated catchment fan systems

space time dynamics of depositional systems experimental evidence and theoretical modeling of heavy tailed statistics 1 in depositional systems channels migrate from one location to another causing erosion and deposition at any given point in the domain the durations of depositional and erosional events as well as their magnitudes control the structure of the stratigraphic record in this study we use high resolution temporal surface elevation data from a controlled experiment to quantify the probability distributions of the processes that govern the evolution of depositional deltaic systems heavy tailed statistics of erosional and depositional events are documented indicating that a small but significant chance exists for the occurrence of extreme events we show that the periods of inactivity when neither deposition nor erosion occurs follow a truncated pareto distribution whose truncation scale is set by the mean characteristic avulsion time scale in the system further we show that the heavy tails in the magnitudes of the erosional and depositional events are not preserved in the stratigraphic record resulting instead in an exponential distribution for the bed sediment thickness it is also shown that the temporal evolution of surface elevation exhibits self similarity with a nonlinear spectrum of scaling exponents multifractality quantifying the complex dynamics of the system finally we show how the results of this study can lead to improved diffusional models for surface evolution using the tools of fractional calculus

fluvial fan deltas linking channel processes with large scale morphodynamics 1 alluvial fan deltas are built by aggrading and avulsing river channels a numerical model of flow and sediment transport in channels is combined with a condition for channel avulsion to describe evolution of the fan surface the model combines elements of two recent approaches 1 diffusional models of depositional basin filling which describe the evolution of overall morphology and 2 cellular models of channel evolution which provide simplified descriptions of channel dynamics here the cellular formulation is used simply as a template for discretizing a standard set of equations describing flow and sediment transport within channels the basic formulation is thus grid invariant and the results are in actual rather than arbitrary time and length scales the model captures the interaction between microscale channel morphodynamics including converging and diverging flow and avulsion and morphodynamics at the macroscale fan it provides a starting point for the study of a wide range of topics including the three dimensional stratigraphy of fan delta deposits and the response of fan deltas to engineering activities

seeing red in cyclic stratigraphy spectral noise estimation for astrochronology 1 fundamental to the development of astronomical time scales is the recognition of oscillatory variability within stratigraphic data and its evaluation relative to a null noise hypothesis in this study monte carlo simulations are used to investigate the suitability of two commonly used noise hypotheses the conventional and robust ar1 approaches and the results highlight important limitations in both for cyclostratigraphic application perhaps most problematic the robust ar1 method can result in inflated confidence level estimates and excessive clumping of false positives within the low frequency portion of the spectrum especially when the underlying noise process has a high lag 1 autocorrelation given typical cyclostratigraphic records this technique will often impose significant eccentricity band variability even in the case of pure ar1 noise an alternative spectral noise estimation method is proposed to overcome these problems which simultaneously allows for departures from the ar1 assumption and obtains high statistical power that is the ability to accurately identify astronomical signals when they are present in the data we apply the method to un tuned 18o data from miocene sediments of the ceara rise indicating statistically significant spectral power at frequencies that are consistent with the published orbital interpretation of weedon et al 1997 furthermore evaluation of the frequency arrangement of the significant spatial bedding periods using the average spectral misfit method for astrochronologic testing reveals that the null hypothesis of no orbital influence can be rejected with a high degree of confidence the 99 8 confidence level

using bar preservation to constrain reworking in channel dominated fluvial stratigraphy fluvial deposits comprising more than 80 channel facies are often thought to have accumulated during intervals of relatively slow subsidence in sedimentary basins this interpretation stems from the conceptual model that migrating and avulsing rivers rework their own deposits during times of limited accommodation creation preferentially removing and bypassing fine floodplain deposits alternatively channel dominated stratigraphy may reflect avulsion patterns that favor channel preservation over floodplain preservation or channel networks fed by sand rich sediment sources that never deposited significant floodplain sediments these potential origins of channel dominated stratigraphy cannot be differentiated without a way of independently assessing how ancient rivers eroded and reworked their own alluvium here we propose a new method that uses fluvial bar preservation as a proxy for reworking in channel dominated stratigraphy we apply this approach to the lower castlegate sandstone upper cretaceous utah usa and use geometric modeling to investigate the degree to which sediment supply and avulsion dynamics influence fluvial deposit preservation castlegate exposures in central utah show up to 80 bar preservation in some localities suggesting that in contrast to previously published interpretations castlegate channel deposits are not heavily reworked and accommodation creation rates during castlegate deposition might have been relatively high model comparisons indicate that well preserved castlegate deposits could have resulted from random avulsions in a rapidly aggrading basin with a sand dominated sediment supply or under lower aggradation conditions if river avulsions avoided previously occupied locations this approach represents a new advance for interpreting the relationships between basin accommodation sediment supply and avulsion dynamics on ancient landscapes and provides a new method for estimating sediment reworking and bypass from ancient river deposits

estimation of completeness of stratigraphical sections using empirical data and theoretical models the completeness of a stratigraphical section is the fraction of time intervals of some specified length t that have left a record a record is left when some sediment is deposited during the interval and is not subsequently eroded a complete section contains no hiatuses longer than t the completeness of a section varies with t and its accumulation rate varies with the length of the time span over which it is measured plots of measured accumulation rate against time span are an empirical means of estimating completeness simple theoretical models help extrapolate meagre data and identify bias completeness at time scale t can depend upon three general properties of the accumulation history the age of the section the long term net accumulation rate drift and the unsteadiness of the sedimentation rate the way unsteadiness is measured depends upon the kinds of fluctuations that can be recognized in the accumulation rate to describe random fluctuations a standard deviation of rates is sufficient one dimensional brownian motion is a model of random fluctuations that explains many aspects of stratigraphical completeness regular periodic fluctuations in accumulation rate may be described in terms of wavelength and amplitude completeness is an increasing function of t drift and in the periodic case the wavelength of fluctuations it decreases with increasing standard deviation of accumulation rate and the amplitude of periodic fluctuations the completeness and thickness of stratigraphical sections are weakly positively associated

long period eccentricity control on sedimentary sequences in the continental madrid basin middle miocene spain article i nfo the middle miocene valdearenas muduex section in the internally drained continental madrid basin central spain is dated bio magnetostratigraphically between 15 2 ma and 11 5 ma the section contains two formation scale sedimentary sequences that both consist of a siliciclastic lower part and a calcareous upper part siliciclastic sedimentation took place in distal floodplain and fluvial environments while limestones resulted from carbonate precipitation in calcic soil profiles and in ephemeral lacustrine water bodies spectral analysis of the l colour time series points to the influence of the 405 kyr and 0 97 myr eccentricity cycles while the bases of the two calcareous intervals correlate to successive minima of the 2 4 myr eccentricity cycle the 405 kyr cycle lags maximum eccentricity whereas the 0 97 and 2 4 myr cycleslag minimum eccentricity each by approximately a quarter of a cycle no obliquity forcing isdetected the observed orbital configuration of 2 4 myr minima at the base of limestone dominated intervals is similar to a previously documented late miocene shift in the teruel basin of northeast spain our results indicate that long period eccentricity clim ate forcing may well be as ignificant player on long tectonic time scales in continental basin fill

scaling the response of deltas to relative sea level cycles by autogenic space and time scales a laboratory study abstract relative sea level rsl change influences surface processes and stratigraphic architecture of deltaic systems and has been studied extensively for decades however we still lack a quantitative framework to define how the magnitude and period of a rsl cycle influences deltaic morphodynamics and the resulting stratigraphy one method for scaling the magnitude and period of rsl cycles is through comparison with the autogenic time and space scales that characterize individual deltaic systems we explore this method using a suite of physical experiments that shared identical forcing conditions with the exception of sea level this approach utilizes two nondimensional numbers that characterize the magnitude and period of rsl cycles magnitude is defined with respect to the maximum autogenic channel depth while the period is defined with respect to the time required to deposit one channel depth of sediment on average everywhere in a basin the experiments include 1 a control experiment lacking rsl cycles used to define autogenic scales 2 a low magnitude long period lmlp stage and 3 a high magnitude short period hmsp stage we observe clear differences in the response of deltas to the forcing in each experiment the rsl cycles in the hmsp stage induce allogenic surface processes and stratigraphic products with scales that exceed the stochastic variability found in the control stage these include the generation of rough shorelines and long temporal gaps in the stratigraphy in contrast the imprint of lmlp cycles on surface processes and stratigraphy is found in properties that define the mean state of a system these include the mean shoreline location and the timing and location of mass extraction from the transport system this work demonstrates the effectiveness of defining the magnitude and period of rsl cycles through autogenic scales and provides insights for generation of forward stratigraphic models influenced by rsl change

prevalence of exponential bed thickness distributions in the stratigraphic record experiments and theory 1 stratigraphy preserved in alluvial basins holds important information for reconstructing past environmental conditions via inversion methodologies in this paper we explore through the use of physical and numerical experiments the forward problem that is we quantify how the probabilistic structure of the processes that govern the evolution of depositional systems relates to the probability distribution of the preserved bed thicknesses we demonstrate that the extreme variability as evidenced by heavy tailed distribution of the surface elevation increments largely cancels itself out in the resulting stratigraphy specifically we show that bed thickness is well described by an exponential distribution even when erosional and depositional increments characterizing the surface evolution exhibit heavy tailed statistics i e large infrequent events have a significant chance of occurrence we attribute this finding to the symmetric nature of the distribution of elevation increments both erosional and depositional events and the additive nature of the stratigraphic filter we also show that the variability of surface elevation increments as measured by the interquartile range of their probability distribution has a robust and well defined relationship with the preserved mean bed thickness

diverse eucritic pebbles in the vaca muerta mesosiderite abstract seven 5 cm basaltic pebbles from the vaca muerta mesosiderite were analyzed by instrumental neutron activation analysis and electron microprobe three additional pebbles were only examined petrographically two pebbles are impact melt breccias four are similar texturally to main group eucrites or some clasts in polymict eucrites three are similar to cumulate eucrites and one is a fragmental breccia similar to certain polymict eucrites cumulate pebbles have extremely low ree concentrations and high eu sm ratios reflecting the virtual absence of intercumulus liquid siderophile interelement ratios in the pebbles are similar to those in vaca muerta metal except for anomalously low ir higher silica and merrillite in the pebbles relative to eucrites may reflect reduction of feo in the silicates by p from mesosiderite metal pebbles were annealed following incorporation into the vaca muerta host impacts were the dominant heat source the occurrence of 20 impact melt breccias among the pebbles and 35 40 melt breccias among mesosiderite whole rocks indicate that mesosiderites were more extensively impact melted than howardites we suggest three alternative models to account for this 1 mesosiderites were derived from a separate parent body that experienced a higher meteoroid fluence than the basaltic achondrite parent body 2 the low velocity accretion of large metallic core fragments from disrupted differentiated asteroids led to metal enrichment of a few regions of the regolith and heat retention in these mesosideritic regions and 3 mesosideritic regolith regions were less likely to be reduced to fine particles by extensive shock than howarditic regions

the stratigraphic filter and bias in measurement of geologic rates 1 erosion and deposition rates estimated from the stratigraphic record frequently exhibit a power law dependence on measurement interval this dependence can result from a power law distribution of stratigraphic hiatuses by representing the stratigraphic filter as a stochastic process called a reverse ascending ladder we describe a likely origin of power law hiatuses and thus rate scaling while power law hiatuses in certain environments can be a direct result of power law periods of stasis no deposition or erosion they are more generally the result of randomness in surface fluctuations irrespective of mean subsidence or uplift autocorrelation in fluctuations can make hiatuses more or less heavy tailed but still exhibit power law characteristics in addition we show that by passing stratigraphic data backward through the filter certain statistics of surface kinematics from their formative environments can be inferred

autocyclic behaviour of fan deltas an analogue experimental study fan deltas are excellent recorders of fan building processes because of their high sedimentation rate particularly in tectonically active settings although previous research focuses mainly on allogenic controls there is clear evidence for autogenically produced storage and release of sediment by flume and numerical modelling that demands further definition of characteristics and significance of autogenically forced facies and stratigraphy analogue experiments were performed on fan deltas with constant extrinsic variables discharge sediment supply sea level and basin relief to demonstrate that fan delta evolution consists of prominent cyclic alternations of channellized flow and sheet flow the channellized flow is initiated by slope induced scouring and subsequent headward erosion to form a channel that connected with the valley while the removed sediment is deposited in a rapidly prograding delta lobe the resulting decrease in channel gradient causes a reduction in flow strength mouth bar formation flow bifurcation and progressive backfilling of the channel in the final stage of channel filling sheet flow coexists for a while with channellized flow semi confined flow although in cycle 1 this phase of semi confined flow was absent subsequent autocyclic incisions are very similar in morphology and gradient however they erode deeper into the delta plain and as a result take more time to backfill the duration of the semi confined flow increases with each subsequent cycle during the period of sheet flow the delta plain aggrades up to the critical gradient required for the initiation of autocyclic incision this critical gradient is dependent on the sediment transport capacity defined by the input conditions these autogenic cycles of erosion and aggradation confirm earlier findings that storage and release of sediment and associated slope variation play an important role in fan delta evolution the erosional surfaces produced by the autocyclic incisions are well preserved by the backfilling process in the deposits of the fan deltas these erosional surfaces can easily be misinterpreted as climate sea level or tectonically produced bounding surfaces

rapid and widespread response of the lower mississippi river to eustatic forcing during the last glacial interglacial cycle the lower mississippi valley provides an exceptional fi eld example for studying the response of a continental scale alluvial system to upstream and downstream forcing associated with the large orbitally controlled glacialinter glacial cycles of the late quaternary however the lack of a numerical chronology for the widespread pleistocene strata assemblage known as the prairie complex which borders the holocene fl oodplain of the lower mississippi river has so far precluded such an analysis here we apply optically stimulated luminescence osl dating mainly on silt sized quartz from prairie complex strata in total 27 osl ages indicate that the prairie complex consists of multiple allostratigraphic units that formed mainly during marine isotope stages 7 5e and 5a thus the aggradation of the prairie complex is strongly correlated with the sea level highstands of the last two glacialinterglacial cycles fluvial incision during the sea level fall associated with the mis 5a mis 4 transition extended as far inland as 600 km from the present day shoreline testifying to the dominant downstream control of fl stratigraphic architecture in the lower mississippi valley in addition the short reaction time of the lower mississippi river suggests that large fl uvial systems can respond much more rapidly to allogenic forcing than is commonly believed

geometric interpretation of time scale dependent sedimentation rates abstract empirical rate data show that aggradation and progradation rates are negatively correlated with the duration they are averaged over this means that we cannot understand deep time sedimentation rates in terms of the abundant rate data we have from modern environments we are addressing this by investigating how growth of a sediment volume in multiple directions affects time averaged accumulation rates that do not necessarily measure all directions of growth we derive a mathematical model from mass balance considerations of a sedimentary deposit that grows without erosion we show that the non linear relationship between the lengths areas and volumes of growing objects require that time averaged sedimentation rates are time scale dependent when a deposit grows in multiple directions we generate rate compilations from simple synthetic stratigraphies which show that we can reproduce the empirical rate compilations by requiring only that deposition occur in a dynamic mosaic of sequential patches in which the areal extent of deposition increases with time scale as described by our mathematical model our model has two implications with application in stratigraphic analysis the first is that it provides a theoretical model of why we cannot expect high stratigraphic completeness if we measure a deposit in fewer directions than it has grown the second is that it provides a framework by which to attribute anomalies in the stratigraphic completeness of a one dimensional or two dimensional sample to scaling effects or erosional hiatuses

experimental steep braided flow application to flooding risk on fans flooding processes occurring on alluvial fans are considerably different from those occurring along single thread rivers with well defined floodplains active erosion rapid sedimentation and the uncertainty in flow path make the prediction of flood evolution and extent difficult based on a large scale experiment this study investigates the long term evolution of the flow on a steep noncohesive sediment surface resembling a complex of merged alluvial fans the results are pertinent to the assessment of flooding hazard on alluvial fans at any given time the average flow occupancy was 21 of the surface however the flow was characterized by active channel switching and overflow processes the percentage of the surface remaining dry was found to decay harmonically with time a reworking time was defined as the time at which half of the surface that was initially dry remained dry whereas the other half was inundated at least once an empirical expression was developed in which reworking time is proportional to the average cross sectional area of flow and inversely proportional to the sediment supply

quantifying the stratigraphic completeness of delta shoreline trajectories understanding the incomplete nature of the stratigraphic record is fundamental for interpreting stratigraphic sequences methods for quantifying stratigraphic completeness for one dimensional stratigraphic columns defined as the proportion of time intervals of some length that contain stratigraphy are commonplace however quantitative assessments of completeness in higher dimensions are lacking here we present a metric for defining stratigraphic completeness of two dimensional shoreline trajectories using topset foreset rollover positions in dip parallel sections and describe the preservation potential of a shoreline trajectory derived from the geometry of the delta surface profile and the kinematics of the geomorphic shoreline trajectory two end member forward models are required to fully constrain the preservation potential of the shoreline dependent on whether or not a topset is eroded during base level fall a laboratory fan delta was constructed under nonsteady boundary conditions and one dimensional stratigraphic column and two dimensional shoreline completeness curves were calculated results are consistent with the hypothesis derived from conservation of sediment mass that completeness over all timescales should increase given increasing dimensions of analysis stratigraphic trajectories and completeness curves determined from forward models using experimental geomorphic trajectories compare well to values from transects when subsampled to the equivalent stratigraphic resolution as observed in the actual preserved sequence the concept of stratigraphic completeness applied to two dimensional trajectory analysis and the end member forward models presented here provide novel tools for a conceptual understanding of the nature of stratigraphic preservation at basin scales

complex network of channels beneath an antarctic ice shelf ice shelves play an important role in stabilizing the interior grounded ice of the large ice sheets the thinning of major ice shelves observed in recent years possibly in connection to warmer ocean waters coming into contact with the ice shelf base has focused attention on the ice ocean interface here we reveal a complex network of sub ice shelf channels under the fimbul ice shelf antarctica mapped using ground penetrating radar over a 100 km2 grid the channels are 300 500 m wide and 50 m high among the narrowest of any reported observing narrow channels beneath an ice shelf that is mainly surrounded by cold ocean waters with temperatures close to the surface freezing point shows that channelized basal melting is not restricted to rapidly melting ice shelves indicating that spatial melt patterns around antarctica are likely to vary on scales that are not yet incorporated in ice ocean models

experimental test of tectonic controls on three dimensional alluvial facies architecture abstract in an extended series of papers by m leeder j r l allen j s bridge j alexander and others the depositional stacking patterns of channel belt deposits were related to tectonic and other external controls we refer to these models collectively as lab models these models established a basic connection between subsidence channel avulsion and the mesoscale channel belt architecture of an alluvial deposit two fundamental predictions resulted from this work 1 channel belt stacking density and hence connectedness is inversely correlated to temporal vertical changes in sedimentation rate and 2 channel belt stacking density and hence connectedness is directly correlated to lateral changes in sedimentation rate in this paper we make use of the experimental earthscape xes facility at the st anthony falls laboratory to examine the effects of temporally and laterally variable subsidence rates on mesoscale alluvial architecture we then compare the experimental results with the main predictions of the early lab models regarding the predictions of the lab models under conditions of high sediment supply and a highly active alluvial system lateral and downstream variation in subsidence geometry and rate have little effect on the details of alluvial architecture we found that the principal architectural signature of changes in subsidence geometry i e laterally variable subsidence rate is stratal tilting and that channel belts are not attracted to the subsidence maximum we hypothesize that the effect of variable subsidence geometry is felt by the fluvial system only if subsidence proceeds faster than the river can adjust to the formation of a topographic low via the deposition of overbank material in the form of splays and sheet sands our results lend impetus to the development of more complete three dimensional numerical models of mesoscale alluvial architecture that couple architecture to broader allogenic forcing mechanisms

geomorphic and tectonic process rates effects of measured time interval analysis of the original numerical components of diverse geomorphic and tectonic process rates indicates that process rate is not independent of measured time interval this implies that direct comparison of geologic process rates measured over variable time intervals may not be valid and that conclusions based on those comparisons regarding changes in rates through geologic time may be misleading in some cases calculation of statistically derived scaling functions is one approach that can be used to account for this measurement interval bias and to improve comparisons of geologic process rate data when this approach is used a 10 4 or 10 5 yr variation in the measured time interval accounts for approximately one order of magnitude change in the measured process rate the magnitude of the correction can substantially affect conclusions of studies that compare uncorrected process rates calculated from variable time intervals

impact melting of the cachari eucrite 3 0 gy ago both the host phase and glass veins of the cachari eucrite have been analyzed by microprobe and neutron activation analysis for their chemical compositions and by mass spectrometry for their 39ar 40ar gas retention ages cachari is chemically similar to other non cumulate eucrites the vesicular glass veins vary from pure glass to devitrified glass to areas that are substantially crystalline the glassy areas have nearly the same concentrations of major and trace elements as the unmelted portions of cachari but some differences probably due to preferential dissolution occur along melt contacts the glass formed by shock melting of cachari host or of rock identical to it 39ar 40ar data for the host and glass suggest distinctly different ages of 3 04 07 gy and 3 47 04 gy respectively the time of glass formation which may also be the time of brecciation is most likely given by the 3 0 gy age of the host the higher age for the glass is interpreted to represent incomplete ar degassing during the 3 0 gy event due to the greater resistance to ar diffusion shown by the glass compared to the host event ages significantly younger than 4 5 gy have now been determined for several eucrites and howardites and suggest a long dynamic regolith history for the parent body

new perspectives on orbitally forced stratigraphy this survey of the current status of research into earth s orbitally forced paleoclimatic record summarizes recent developments in the theory of earth s orbital parameters and reviews how various techniques of data collection and analysis have fared in the search and recovery of orbital signals in ancient stratigraphy the emerging significance of the quasi periodicity of earth s orbital variations as a prin cipal tool in the analysis of orbitally forced stratigraphy is discussed in detail five case studies are presented that illustrate new directions in research a time series analysis of discontinuous strata b measurement of ultra high resolution stratigraphic signals c new perspectives on the 100 kyr pleistocene glaciation problem d strati graphic evidence for solar system resonance modes and e evaluating phanerozoic length of day from orbitally forced stratigraphy the study of how earth s orbital parameters came to be recorded in ancient stra tigraphy has recently moved into a new phase of scientific inquiry and discovery notable advances in celestial mechanics and in the analysis of stratigraphic data have given rise to new ways of solving old problems and have uncovered new problems for the first time new tools have facilitated the recovery of extended high resolution orbital signals from stratigraphy advanced analytical techniques have now been fully incorporated into the field an updated theory of earth s orbital parameters provides an accurate ephemeris for the past 16 million years for precision correlation between earth s orbital parameters and orbitally forced stratigraphy some orbital eccentricity modes can be used for orbital stratal cal ibrations to several hundred million years ago these breakthroughs have transformed the study of orbitally forced stratigra phy into an applied field that addresses long standing problems in disciplines as far ranging as geochronology geodynamics and astrodynamics orbital signals provide the framework for a high resolution orbital chronostratigraphy as far back