kinematic models of fluvial terraces over active detachment folds constraints on the growth mechanism of the kashi atushi fold system chinese tian shan during detachment folding the relationship between differential uplift and shortening depends on the mechanism of fold growth such as limb rotation or hinge migration and may vary over the lifetime of a fold thus neither long term shortening rates nor the present fold geometry unambiguously constrain the kinematics of fold growth where rivers cut through growing anticlines flights of abandoned fluvial terraces act as passive kinematic markers as shortening progresses the terraces become deformed and thereby preserve critical information about the kinematics and evolution of active fold growth to constrain recent fold growth across three detachment folds in the kashi atushi fold system in the sw tian shan china we surveyed flights of deformed terraces and compared them with geometric models of successively emplaced horizontal unconformities terraces across pregrowth strata deformed by hinge migration limb rotation and a combination of the two migration of angular hinges and curved hinge zones were also compared each kinematic model predicts both a distinct geometry for the deformed terraces and contrasting angular relationships between the terraces and the pregrowth strata notably limb rotation and migration of curved hinge zones result in progressively rotated terraces that cut across pregrowth strata whereas all limb lengthening models result in parallelism between pregrowth strata and terrace straths across much of the fold the kashi atushi terraces show clear evidence of abandoned axial surfaces concentrated deformation near the core of the folds and progressive tilting with age when compared to the model predictions the folds are likely growing by a combination of limb rotation in the tight cores of the folds and hinge zone migration of pregrowth strata across the flanks of the folds

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

an abyssal carbonate compensation depth overshoot in the aftermath of the palaeocene eocene thermal maximum the palaeocene eocene thermal maximum was associated with a massive release of carbon marine sediments suggest a temporary deepening of the calcite compensation depth indicating extensive silicate weatheringin the aftermath of the event the palaeocene eocene thermal maximum was associated with a massive release of carbon marine sediments suggest a temporary deepening of the calcite compensation depth indicating extensive silicate weatheringin the aftermath of the event during the palaeocene eocene thermal maximum petm about 56 million years ago thousands of petagrams of carbon were released into the atmosphere and ocean in just a few thousand years followed by gradual sequestration over approximately 200 000 years if silicate weathering is one of the key negative feedbacks that removed this carbon a period of seawater calcium carbonate saturation greater than pre event levels would be expected during the event s recovery phase in marine sediments this should be recorded as a temporary deepening of the depth below which no calcite is preserved the calcite compensation depth ccd previous and new sedimentary records from sites that were above the pre petm ccd show enhanced carbonate accumulation following the petm a new record from an abyssal site in the north atlantic that lay below the pre petm ccd shows a period of carbonate preservation beginning about 70 000 years after the onset of the petm providing the first direct evidence for an over deepening of the ccd this record confirms an overshoot in ocean carbonate saturation during the petm recovery simulations with two earth system models support scenarios for the petm that involve a large initial carbon release followed by prolonged low level emissions consistent with the timing of ccd deepening in our record our findings indicate that sequestration of these carbon emissions was most likely the result of both globally enhanced calcite burial above the ccd and at least in the north atlantic an over deepening of the ccd

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

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

astronomically controlled cycles in the lower tertiary of gubbio italy abstract a grouping of marl limestone beds in the tertiary of gubbio is interpreted in terms of sedimentary cycles two methods of recording are used subjective mapping of cycle boundaries in the field and power spectral analysis of bed thickness measurements both result in cycle thicknesses of between 30 and 70 cm the cycle record is compared with the known magnetic stratigraphy and this gives an absolute time estimate of 100 kyr for the cycle it therefore seems likely that the earth s eccentricity period is the ultimate cause of the cycle

a quantitative approach to understanding dated dune stratigraphies attempts to reconstruct past changes in climate related forcing of dryland landscapes are hampered by the lack of an adequate quantitative framework for understanding the production and interpretation of dated sedimentary records in drylands as in other environments information on past forcing conditions is progressively modified degraded and removed from the available stratigraphic record by a series of filters involving changes in the primary forcing factors themselves geomorphological processes and the sampling dating procedures in this paper we describe a quantitative model that includes these effects and use the model to examine the nature of preserved dryland sedimentary records and their relationships to primary forcing conditions thicker preserved sedimentary records reflect periods of more intense aeolian activity localized switching between erosion and deposition results in discontinuous and highly variable stratigraphic sequences a preservation bias towards younger deposits is observed potentially leading to a continuum of accumulation that decays approximately in proportion to time periods not represented by deposition can in some cases be interpreted as periods of higher precipitation and or lower wind energy an asymmetry exists between the efficiency with which past drier and wetter episodes can be identified which relates to the time separation of depositional periods and the correct distinction between hiatuses due to forcing conditions and those due to under sampling relevant to this is the effect of random dating errors statistical uncertainty which increasingly with age filter out higher frequency events from the record a new data treatment method termed accumulation rate variability provides an efficient proxy for accumulation rates and therefore the intensity of aeolian activity with significant improvements over existing date frequency methods the filtering problem discussed applies to all attempts at understanding the timing and nature of past events independent of the proxies and dating methods employed further explicit analysis of these issues would be beneficial copyright 2013 john wiley sons ltd

cenozoic tectonics in the urumgi korla region of the chinese tien shan cenozoic deformation within the tien shan of central asia has accommodated part of the post collisional indentation of the indian plate into asia within the urumgi korla region of the chinese tien shan this occurred dominantly on thrusts with secondary strike slip faulting the gross pattern of deformation is of moderate to steeply dipping thrusts that have overthrust foreland basins to the north and south of the range the junggar and tarim basins respectively smaller foreland basins lie within the margins of the range itself turfan chai wo pu korla and qumishi basins these lie in the footwalls of local thrust systems both the turfan and the korla basins contain major thrusts within them they are complex foreland basins deformation has progressively affected regions further into the interior of the junggar basin and propagated into the interiors of the intermontane basins no unidirectional deformation front has passed across the tien shan in the neogene and quaternary an oligocene unconformity may indicate the time of the onset of the cenozoic deformation but most of the cenozoic molasse has been deposited after the palaeogene the rate of deposition in basins next to the uplifted ranges has increased since the onset of deformation there has been at least about 80 km of cenozoic shortening across this part of the tien shan cenozoic shortening is greater in sections of the range further west these are nearer to the northern margin of the indian indenter cenozoic compression has reactivated structures created by the two late palaeozoic collisions that created the ancestral tien shan these palaeozoic structures have exerted a strong control over the style and location of the cenozoic deformation

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

a geologically constrained monte carlo approach to modeling exposure ages from profiles of cosmogenic nuclides an example from lees ferry arizona we present a user friendly and versatile monte carlo simulator for modeling profiles of in situ terrestrial cosmogenic nuclides tcns our program available online at http geochronology earthsciences dal ca downloads models html permits the incorporation of site specific geologic knowledge to calculate most probable values for exposure age erosion rate and inherited nuclide concentration while providing a rigorous treatment of their uncertainties the simulator is demonstrated with 10be data from a fluvial terrace at lees ferry arizona interpreted constraints on erosion based on local soil properties and terrace morphology yield a most probable exposure age and inheritance of 83 9 14 1 19 1 ka and 9 49 2 52 1 21 104 atoms g 1 respectively 2 without the ability to apply some constraint to either erosion rate or age shallow depth profiles of any cosmogenic nuclide except for nuclides produced via thermal and epithermal neutron capture e g 36cl cannot be optimized to resolve either parameter contrasting simulations of 10be data from both sand and pebble sized clasts within the same deposit indicate grain size can significantly affect the ability to model ages with tcn depth profiles and when possible sand not pebbles should be used for depth profile exposure dating

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

condensation processes in shallow platforms abstract sequence stratigraphy allows elucidation of the time space relationships of deposits in sedimentary basins however the relative distribution of unconformities and condensed sections can neither be used as diagnostic criteria for particular palaeogeographic settings nor as indicators of maximum regional transgressions condensation processes also occur in the shallowest portions of platforms and during maximum regression episodes three separate processes of condensation are here distinguished stratigraphic sedimentary and taphonomic these three categories of condensation can be used to analyze patterns of sediment distribution and also to estimate lateral and vertical variations in sedimentation rates contrary to the usual interpretation the maximum values of rate of sedimentation and degree of accommodation of sediments as well as the highest relative sea level occur in the lowest levels of the shallowing upward sequences the distinction between these condensation processes allows one to predict that the degree of sedimentary and stratigraphic condensation will be higher towards the distal portions of the platforms whereas the stratigraphic condensation processes without sedimentary condensation will show the maximum intensity and frequency in the shallowest portions of the platforms

numerical forward modeling of carbonate platform dynamics an evaluation of complexity and completeness in carbonate strata abstract it is clear that carbonate strata are complex and incomplete but the nature and origins of the complexity and the origin and distribution of hiatuses remain poorly understood a three dimensional numerical forward model of carbonate platform systems has been used to investigate how variations in complexity and completeness arise in carbonate strata the model includes depth dependent carbonate production occurring as a stochastic mosaic of producing elements across a topographic surface it also includes depth dependent sediment erosion transport and deposition governed by a regional transport direction that can vary stochastically through time and by wave refraction that causes local variations in transport direction combined mosaic production and variable sediment transport create a complex distribution of prograding islands generating self organizing shallowing upward parasequences of variable thickness and variable lateral extent hiatuses occur throughout the parasequences not just at the base and top generated by nondeposition due to mosaic production and by erosional scour this erosion is triggered by variations in water depth and fetch distance created by complex island morphologies preserved strata represent between 15 and 60 of total elapsed time measured at a 2 ky resolution and much of the preserved thickness represents punctuated deposition with depositional events spanning only a few thousand years stratigraphic completeness depends on subsidence rate and sediment transport rate so that completeness generally increases with increasing subsidence rate and decreasing transport rate but shows a nonlinear relationship with subsidence rate this suggests that reliable estimates of completeness of ancient carbonate strata require more than knowledge of subsidence rate and sea level change particularly because the real situation is likely to be considerably more complex than represented in this model the stochastic production mosaic and stochastic variations in regional transport direction create complex strata whereas the self organizing island progradation process creates simpler ordered strata a combination of the two processes creates an intermediate level of complexity producing strata consisting of laterally impersistent parasequences with numerous erosion surfaces and complex stacking patterns and complex thickness distributions this has important implications for parasequence correlation in outcrop and the subsurface

middle jurassic magnetopolarity stratigraphy of a well core from the brent group north sea abstract a magnetopolarity stratigraphy has been constructed by detailed palaeomagnetic investigations of a well core covering the middle jurassic brent group north sea these high time resolution results have provided a chronostratigraphic framework which has been correlated tentatively with the reported magnetopolarity stratigraphy based on a pelagic limestone sequence from caracabuey southern spain biostratigraphic datings suggest the same age span as the magnetopolarity results the sediments which range from mudstone to coarse sandstone have a very low content of ferrimagnetic minerals remanent coercivity analysis suggests that magnetomineralogy is facies and grain size independent and pyrrhotite is the most likely main magnetic remanence carrying mineral palaeomagnetic analysis of the core specimens indicates mostly multicomponent magnetization the characteristic remanent magnetization is inferred to be a combination of post depositional detrital remanent magnetization and a dominant early chemical remanent magnetization

variability of sedimentary sequence numerical modeling of the deposition erosion process reinterpretation of field studies of bedload transport allowed some power law relations to be obtained between different quantities they were taken as a basis for the construction of a numerical model simulating bedload transport the deposition erosion process is presented as a sequence of individual events with intensities distributed according to a power law characteristic of the regime of self organized criticality the model output sedimentary cross sections with the model age of each of its elements is rich in features resulting from the non linearity of the underlying process analysis of the results of a series of numerical experiments provided an estimation of scale invariance of model sedimentary structures in space and time these data are tested against observed regularities of spaciotemporal variability of real sedimentary sequences good agreement of these data makes it possible to extrapolate the scaling relations obtained to larger scales

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

climatic and eustatic signals in a global compilation of shallow marine carbonate accumulation rates two of the most important factors that control the accumulation rate of material in carbonate platform environments on geological time scales are climate and eustasy accurately assessing the importance of these interrelated factors through the study of both modern and ancient carbonate facies however is problematic these difficulties arise from both the complexities inherent in carbonate depositional systems and the demonstrable incompleteness of the stratigraphic record here a new compilation of more than 19 000 global phanerozoic shallow marine carbonate accumulation rates derived from nearly 300 individual stratigraphic sections is presented these data provide the first global holistic view of changes in shallow marine carbonate production in response to climate and eustasy on geological time scales notably a clear latitudinal dependence on carbonate accumulation rates is recognized in the data moreover it can also be demonstrated that rates calculated across the last glacial maximum and holocene track changes in sea level in detail the data show that globally averaged changes in carbonate accumulation rates lagged changes in sea level by ca 3 kyr reflecting the commonly observed delay in the response of individual carbonate successions to sea level rise differences between the rates of carbonate accumulation and sea level change over the past 25 kyr ostensibly reflect changing accumulation mode with platform drowning give up mode pervasive during peak early holocene sea level rise followed by a switch to catch up mode accumulation from ca 9 ka to the present carbonate accumulation rates older than the quaternary are typically calculated over time spans much greater than 100 kyr and at these time spans rates primarily reflect long term tectonically mediated accommodation space changes rather than shorter term changes in climate eustasy this finding coupled with issues of stratigraphic incompleteness and data abundance tempers the utility of this and other compilations for assessing accurately the role of climate and eustasy in mediating carbonate accumulation rates through geological time

ordered hierarchy versus scale invariance in sequence stratigraphy sequence stratigraphy has been applied in a wide range of scales of time and space from decimeter thick layers formed within hours to kilometer thick basin fills formed during hundreds of millions of years the traditional approach to practice sequence stratigraphy in this wide range of scales is to subdivide the sediment piles into an ordered hierarchy of sequence cycles of different duration and different architecture an alternative are scale invariant models with fractal characteristics published data confirm two predictions of the ordered hierarchy model sequences of very short duration 200 106 years are symmetrical transgressive regressive cycles however the sequence record in the range of 1 104 200 106 years the principal domain of sequence stratigraphy shows a rather irregular succession of sequences with variable symmetry and bounded by flooding surfaces or exposure surfaces for these time scales scale invariant models are a good first approximation particularly because the evidence for scale invariance and randomness in the stratigraphic record is strong frequency spectra of sea level change as well as rates of sedimentation and rates of accommodation change plotted against length of observation span show basic trends indistinguishable from random walk these trends combined with scale invariant sequence models may be the most efficient tools for across the board predictions on sequences and for locating islands of order in the sequence record

review stratigraphy meta stratigraphy and chaos an alternative approach to stratigraphic analysis is proposed it takes as its starting point the simple general characteristics of the stratigraphic record and the complex chaotic behaviours of the systems that combine to generate this record in this context smith s stratigraphy machine sm concept is developed the sm is a chaotic global system combining the operations of the atmosphere hydrosphere lithosphere and asthenosphere which everywhere tends to self organize towards a critical state in which continuous loading of the system with rock waste over time is balanced by the unloading that creates the record the outputs of the sm are simple and nonscale dependent in character with residence times in the record ranging from a second or less to 1 billion years however only those long lived in the human time frame are judged to be of stratigraphic significance and the range of residence times entails that the stratigraphic record embraces a similar range of hiatuses or gaps the value of the sm as developed here is that it can be regarded as a meta stratigraphic concept that transcends the usual frameworks of stratigraphic classification and interpretation and thus allows a reappraisal of significant features of the record such as its perceived cycles and sequences there are three outcomes of this meta stratigraphic analysis first the geometric units employed in sequence stratigraphy are components of a self similar series of essentially lenticular bodies with no fundamental characteristics to distinguish them from larger and smaller bodies in the generally self similar series secondly the interactions and feedbacks within the sm are so complex and its outputs so repetitive in general character that it is dangerous to assume that any perceived cyclicity provides an unambiguous chronicle of process cyclicity whether eustatic climatic or tectonic the classic coarsening upward cyclicity of shallow marine facies can for example be viewed solely as the outcome of the lack of phasing between the chaotic behaviours tending to unload the sm and those creating accommodation space finally the meta stratigraphic approach reinforces the view that in the absence of demonstrable stratal continuity chronostratigraphic correlation must continue to rely on sample based mainly biostratigraphical methods rather than sequence stratigraphy

magnetostratigraphy of the middle jurassic brent group in the oseberg oil field northern north sea abstract magnetopolarity stratigraphy of the brent group and the uppermost part of the dunlin group has been established in two well cores from the oseberg field well 30 6 7 and well 30 9 2 northern north sea palaeomagnetic analysis of thermal demagnetization results defines a series of normal and reverse magnetozones in both wells remanent coercivity analysis of these middle jurassic clastic sediments indicates a magnetomineralogy independent of grain size interpreted to be of diagenetic origin thus suggesting that the magnetization is of early post depositional origin integration with the existing palynostratigraphic framework results in the establishment of several isochronous horizons especially in the ness formation which suggests lateral continuity of magnetostratigraphic datum planes between the two wells at the oseberg field although the exact dating of the magnetozones is not established the combined application of magnetopolarity and biostratigraphy provides a stratigraphic framework of improved resolution for these rock formations

cantor set model of eolian dust deposits on desert alluvial fan terraces available data show that eolian dust accumulation rates on desert alluvial fan terraces are often inversely proportional to the square root of the terrace age for a given area this temporal scaling is similar to that observed in fluvial and marine stratigraphic sequences in which a fractal distribution of hiatuses occurs i e a cantor set eolian dust accumulation on alluvial fan terraces is controlled by regional climatic influences on dust deposition e g dessication of pluvial lakes in the early holocene and local surface characteristics e g vegetation and pavement coverage that control dust preservation in order to interpret the observed scaling in terms of these relative influences i consider two end member models 1 a deterministic model in which dust deposition is controlled by cyclical climatic changes i e glacial interglacial cycles and in which no erosion occurs and 2 a stochastic model in which erosion and deposition take place with equal probability and magnitude during each time step i e a bounded random walk the observed temporal scaling is most consistent with the bounded random walk model suggesting that long term eolian dust accumulation is predominantly controlled by episodic changes in vegetation and pavement coverage over time and that eolian dust deposits are strongly punctuated by episodes of erosional reworking at a wide range of temporal scales

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

rates of sedimentation and stratigraphical completeness the most obvious result of sedimentation processes is the change in the thickness of accumulated sediment with time whenever the net change over a period of time is positive a record is left of a sedimentation system s existence a stratigraphical section for the stratigrapher the problem that such a section poses is to determine the detailed correspondence of thickness to time1 for the sedimentologist the problem is to infer the nature of the parent sedimentation system and to estimate its parameters a simple stochastic model is used here 1 to illustrate some basic stratigraphical results of clastic sedimentation processes 2 to offer an explanation for the commonly cited systematic decrease of mean sedimentation rate with increasing time span and 3 to assess the concept of stratigraphical completeness it will be assumed that all post depositional non erosional processes such as compaction can be identified and their effects on stratigraphical thickness allowed for

depo sequence as tool to convert shoreline trajectory from space domain to time domain abstract deposystems are complex and governed by discrete depo events with variable intervals of stasis or erosion in between since shoreface sediments indicate sea level depo events of shoreline facies are discrete samples of sea level only if these samples are sufficiently regular and frequent will the shoreline trajectory in the space domain accurately reflect the sea level curve in the time domain this study presents a method to convert shoreline trajectory in the space domain to sea level curve in the time domain from artificial miniature deltas one obtains the depo sequence as function of time and uses it to convert depo sequence from time to space domain correlate depo sequence to shoreline trajectory in the space domain and convert shoreline trajectory from space to time domain for natural deltas one would extract the depo set in the frequency domain i e the probability density function of stasis intervals between depo events from the experimental depo sequence and use it to convert shoreline trajectory from space to time domain and infer a range of possible sea level curves this method therewith explicitly includes the uncertainty of the inferred sea level curve

fluvial processes and cyclicity in terminal fan deposits an example from the late devonian of southwest ireland abstract the gun point formation is a sandstone dominated sequence approximately 1 5 2 5 km thick which forms part of a major 6 km late devonian alluvial basin fill succession in southwest ireland it is interpreted as the deposits of a southerly flowing terminal fan system which operated under a semi arid climate the proximal zone was characterized by low sinuosity gravelly feeder channels which passed downstream into a medial zone dominated by a sandy braidplain further south in the distal zone phases of high energy flood activity were centred on transient low sinuosity ephemeral channels and were separated by more quiescent periods of shallow sheetflooding subaerial exposure and non deposition sedimentary parameters such as set thickness coset thickness channel sand body density and maximum sand body thickness all exhibit regular cyclic fluctuations with a periodicity of 160 180 m the cycles are interpreted as evidence of regular discharge variations which may have been a response to the 412 ka orbital eccentricity cycle a second periodicity of approximately 700 m has also been detected and is thought to reflect long term variations in basin subsidence

a fractal model for the distribution of stratigraphic hiatuses several recent studies have suggested that there is a negative log linear relationship between sedimentation rates and the time span over which they are measured i e measured sedimentation rates are slow when measured over long time spans and rapid when measured over short time spans this relationship may be due to the inclusion of more and longer hiatuses over long time spans this paper proposes a mathematical model consistent with this relationship that is based upon the fractal cantor bar this model allows the estimation of the relative number and durations of stratigraphic hiatuses within a given section

uplift and active tectonics of southern albania inferred from incision of alluvial terraces abstract in albania the osum and vjoje rivers cross the active graben system and the active frontal thrust system of the albanides the effects of climatic and geodynamic forcing on the development of these two rivers were investigated by the means of field mapping topographic surveying and absolute exposure age dating we established the chronology of terraces abandonment from the compilation of new dating 14c and in situ produced 10be and previously published data we identified nine fluvial terraces units developed since marine isotope stage 6 up to historic times from this reconstituted history we quantified the vertical uplift on a time scale shorter than the glacial climatic cycle regional bulging produces an overall increase of the incision rate from the west to the east that reaches a maximum value of 2 8 m ka in the hinterland local pulses of incision are generated by activation of normal faults the most active faults have a sw ne trend and a vertical slip rate ranging from 1 8 to 2 2 m ka this study outlines the geodynamic control in the development of rivers flowing through the albanides on the scale of 103 105ka

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

optimizing significance testing of astronomical forcing in cyclostratigraphy the recognition of astronomically forced milankovitch climate cycles in geological archives marked a major advance in earth science revealing a heartbeat within the climate system of general importance and key utility power spectral analysis is the primary tool used to facilitate identification of astronomical cycles in stratigraphic data but commonly employed methods for testing the statistical significance of relatively high narrow band variance of potential astronomical origin in spectra have been criticized for inadequately balancing the respective probabilities of type i false positive and type ii false negative errors this has led to suggestions that the importance of astronomical forcing in earth history is overstated it can be readily demonstrated however that the imperfect nature of the stratigraphic record and the quasiperiodicity of astronomical cycles sets an upper limit on the attainable significance of astronomical signals optimized significance testing is that which minimizes the combined probability of type i and type ii errors numerical simulations of stratigraphically preserved astronomical signals suggest that optimum significance levels at which to reject a null hypothesis of no astronomical forcing are between 0 01 and 0 001 i e 99 99 9 confidence level this is lower than commonly employed in the literature 90 99 confidence levels nevertheless in consonance with the emergent view from other scientific disciplines fixed value null hypothesis significance testing of power spectra is implicitly ill suited to demonstrating astronomical forcing and the use of spectral analysis remains a difficult and subjective endeavor in the absence of additional supporting evidence

wavelet analysis of well logging data from oil source rock egret member offshore eastern canada wavelet analysis is a sensitive method for automatically detecting and distinguishing abrupt discontinuities i e faults unconformities cyclicity and gradual changes in sedimentation rate by transforming depth related sedimentary signals i e gamma rays into wavelengths at distinct depth intervals we used wavelet analysis for evaluation of the spatio temporal distribution of oil source rocks and for estimating accumulation rates in a sedimentary basin having high resolution the method was applied to 16 gamma ray logs from the jurassic egret member an oil source rock succession 55 m to 227 m in thickness offshore eastern canada dominant gamma ray cycles having wavelengths varying from 2 8 m western margin of the basin to 24 m eastern part of the basin have been detected by wavelet analysis the coincidence of the ratio of predominant gamma ray cycles with the ratio of milankovitch spectra about 400 100 40 20 k y suggests that climatic cycles are an important factor controlling sedimentary cyclicity in the egret member dominant wavelengths likely represent 100 k y eccentricity giving accumulation times of 1 9 m y for stratigraphically complete sections having 19 successive 2 8 m gamma ray cycles and giving accumulation times of 600 k y for incomplete successions having only 6 cycles up to four discontinuities occur in gamma ray log cyclicity and separate the egret member into subunits we interpret the discontinuities as unconformities or faults and as related to sediments having low petroleum potential the stratigraphic completeness of the egret member is correlated to total mass of organic carbon and decreasing thickness of non source rock intervals having correlation coefficients of r 0 8 and r 0 76 respectively

completeness of the geological record the completeness of a sedimentary section of known timespan may be assessed qualitatively by comparing its thickness with the average accumulation for that timespan average accumulations may be estimated from sediment volume and continental area data quantitative completeness estimation methods based on data compiled from the geological literature have been proposed but we argue that the literature data are significantly biased and cannot support such methods interestingly however a comparison of the literature data and accumulation averages computed from sediment volume data suggests that the thickest known sections may be extremely complete

reconstructing morphological and depositional characteristics in subsurface sedimentary systems an example from the maastrichtian danian ormen lange system more basin norwegian sea understanding large scale sediment distribution patterns and morphological characteristics in subsurface sedimentary systems is highly challenging and generally requires regional seismic and well coverage here we test a method that aims to predict first order morphological characteristics and type of sedimentary transport system in ancient source to sink systems based on trends observed in submodern pliocene holocene depositional environments an example from the paleocene ormen lange system more basin norwegian sea demonstrates the application of the method and several descriptive parameters are estimated for this ancient subsurface system in the ormen lange system basin floor fan and distal slope parameters are well constrained from seismic and well control however knowledge of the morphology and relationships between upper slope shelf and catchment characteristics and their relationships to deep water systems is poor and these are the parameters that are discussed in this study estimated parameters of catchment size derived from this technique are in good agreement with preserved remnants of fluvial valleys located onshore predicted sediment transport characteristics are also comparable to the depositional mechanisms interpreted from cores and well logs suggesting a small tectonically active system with high fluvial discharge and low sediment storage potential in the catchment and shelf subenvironments the discussed method is thus capable of predicting first order segment characteristics in subsurface sedimentary systems with an uncertainty of one to two orders of magnitude this information can be used to increase the understanding of unexplored basins or to add data and uncertainty ranges to well known petroleum systems

a new method for interpolating ages between calibrated control points based on foraminiferal concentrations abstract the new method relies on the assumption that foraminiferal accumulation rates are uniform or are at least steadier than bulk sediment accumulation rates over the time scale of intervals between calibrated control points where this condition is fulfilled interpolated ages can be assigned to sampled horizons n in each age bracketed interval by apportioning the difference in ages between control points at the bottom and top of each age bracketed interval t to samples in each interval this is done on the basis of the proportional subdivision of the sum total of weight standardized counts of foraminifera cn in each interval which can be simply expressed as t cn cn the new method is described here in relation to well cuttings samples but it can be adapted for use with whole rock samples from cores and outcrops a case study of the pukearuhe 1 well demonstrates the method its application and outputs in relation to deep water miocene age strata in taranaki basin new zealand the study of this well shows that foraminiferal accumulation rates may not be a precise guide for elapsed time but in tectonically active basins and in settings on the margins of basins where foraminiferal concentrations can be shown to be regulated by influxes of siliciclastic sediment it is better to interpolate ages between calibrated control points on the basis of a uniform foraminiferal accumulation scale than a uniform bulk sediment accumulation scale

estimating stratigraphic completeness the completeness of a stratigraphic section is difficult to estimate in practice because stratigraphic completeness is a measure that is based entirely in time the suggestion that the stratigraphic completeness of a section of known timespan might be estimated by comparing that section s thickness against the global average thickness of sediment accumulated in that timespan would thus be of immense practical value if only that relationship between completeness and thickness could be demonstrated regrettably there appears to be insufficient data to warrant this assertion

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

detection of sedimentary cyclicity and stratigraphic completeness by wavelet analysis an application to late albian cyclostratigraphy of the western canada sedimentary basin abstract on the basis of the time frequency scaling property of the wavelet transform accumulation rates and stratigraphic completeness can be calculated for various observation time spans ot by using wavelet analysis wavelet analysis also allows automatic detection of high frequency sedimentary cyclicity and abrupt and gradual variations in sedimentation rate the preservation of different frequency cycles is strongly dependent on variations of the intensity to noise ratio of the original cycles and accumulation rate through time as demonstrated by computer models wavelet analysis was used to detect and correlate periodic cyclic successions of marine sediments in the western canada sedimentary basin in observation time spans ranging from 100 kyr to 3 8 myr cycles in gamma ray data are in accordance with sonic logging lithology and biotic change cyclic units embedded in the upper albian westgate and joli fou formations are almost periodic with 11 and 10 repetitions respectively accumulation rates at ot 100 kyr vary from 5 7 cm kyr in mudstone successions to 29 cm kyr in sandstone successions of the rocky mountains foothills these 100 kyr cycles are preserved from 30 in the manitoba escarpment to 100 in se alberta in the westgate formation these cycles can be correlated throughout facies belts of siliciclastic sedimentation in the entire basin in gamma ray logging the cyclicity is most pronounced in the foredeep succession and almost without fluctuations in the basin center cyclic changes from wet to dry climate probably forced by milankovitch cycles of 100 kyr eccentricity may have controlled the stable periodic sedimentary cyclicity

concepts of sediment deposition and accumulation applied to the continental shelf near the mouth of the yangtze river a fundamental understanding of how sedimentary strata form requires distinction between deposition and accumulation of particles deposition refers to the temporary emplacement of particles on the seabed accumulation is the net sum of many episodes of sediment deposition and removal the difference between rates of deposition and accumulation affects the ability of an environment to record sedimentary events radionuclide profiles of 234 th and 210 pb within the seabed can be used to determine 100 day deposition rates and 100 yr accumulation rates respectively on the continental shelf near the mouth of the yangtze river short term deposition rates are about 4 4 cm month whereas accumulation rates integrated over a century are an order of magnitude less about 5 4 cm yr

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

a new look at sedimentation rates and the completeness of the stratigraphic record several recent papers have suggested that completeness of stratigraphic sections can be estimated by using the ratio of long term sedimentation rates to short term rates we show that the median short term sedimentation rates used in these papers are erroneous and are mostly an artifact arising from improper data manipulation to demonstrate the artificial character of short term median rates we have generated a series of plots assuming a constant sedimentation rate with fixed variance and defined limits of measurement precision these plots demonstrate that increasing variance in the time required to deposit sediments will result in spuriously high short term median sedimentation rates a new method for calculating median sedimentation rates which eliminates the problem of spurious median rates is then applied to make an improved estimate of expected completeness recalculated median values show that sedimentation rates for pelagic sediments are close to identical for both short term and long term tim

across shelf sediment transport since the last glacial maximum southern california margin correlation of continental shelf slope stratigraphy in santa monica bay southern california with ocean drilling program records for nearby slope basin sites has illuminated the timing and scale of terrigenous sediment dispersal on margin since the last glacial maximum lgm marine flooding surfaces preserved in a transgressive sequence on the santa monica shelf provide a key link between base level elevation and sediment transport across shelf sediment accumulation rates at slope basin sites were maximal ca 15 10 ka well after the lgm decreased during the 12 9 ka transition from fluvial estuarine to fully marine conditions on the shelf and decelerated throughout the holocene to 30 75 of their values at the lgm the deceleration is interpreted to manifest a landward shift in the margin depocenter with the onset of transgressive sedimentation beginning when sea level surmounted the shelf edge ca 13 ka as predicted by sequence stratigraphic models however the records make clear that factors other than base level modulated slope basin accumulation rates during the deglaciation

cyclostratigraphy stratigraphic gaps and the duration of the hettangian stage jurassic insights from the blue lias formation of southern britain the lithostratigraphic characteristics of the iconic blue lias formation of southern britain are influenced by sedimentation rates and stratigraphic gaps evidence for regular sedimentary cycles is reassessed using logs of magnetic susceptibility from four sites as an inverse proxy for carbonate content standard spectral analysis including allowing for false discovery rates demonstrates several scales of regular cyclicity in depth bayesian probability spectra provide independent confirmation of at least one scale of regular cyclicity at all sites the frequency ratios between the different scales of cyclicity are consistent with astronomical forcing of climate at the periods of the short eccentricity obliquity and precession cycles using local tuned time scales 62 ammonite biohorizons have minimum durations of 0 7 to 276 ka with 94 of them

self organized complexity in geomorphology observations and models the focus of this paper is to relate fundamental statistical properties of landforms and drainage networks to models that have been developed in statistical physics relevant properties and models are reviewed and a general overview is presented landforms and drainage networks are clearly complex but well defined scaling laws are found coastlines topography contours and lakes are classic self similar fractals the height of topography along a linear track is well approximated as a brownian walk a self affine fractal this type of behavior has also been found in surface physics for example the surface roughness of a fracture an applicable model is the langevin equation the heat equation with a stochastic white noise driver this model also reproduces the statistics of sediment deposition drainage networks were one of the original examples of self similar fractal trees an important advance in quantifying the structure of drainage networks is the application of the tokunaga fractal side branching statistics a classic problem in statistical physics is the diffusion limited aggregation the resulting tree like structures have been shown to also satisfy the tokunaga statistics a modified version of the diffusion limited aggregation model reproduces the statistics of drainage networks it is concluded that the models developed in statistical physics have direct applicability to the fundamental problems in geomorphology

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

measured rates of sedimentation what exactly are we estimating and why abstract data on rates of sedimentation are essential in studies of sedimentation systems these data are obtained in three main study contexts 1 the study of sedimentation systems that are active today 2 the source to sink study of sedimentation systems that no longer are active and 3 the study of the relationship between accumulation rate and measurement timespan the aim of this paper is to question the meaning of measured rates of sedimentation and their interpretability particularly in these three contexts individual measurements of rate of sedimentation must always be interpreted with care firstly there are different definitions for instance with different statistical support or measurement dimension values that are defined differently cannot be compared directly secondly appropriate sampling schemes must have been used for the measurement this minimises sampling bias thirdly the inherent limitations of the data sources must be taken into account rates of sedimentation can usually be measured successfully in active sedimentation systems the same is not true for systems that are no longer active these can only be studied using the stratigraphic successions left behind rates of erosion can never be measured successfully in stratigraphic successions rate of sedimentation is essentially a ratio an amount of sedimentation per length of time therefore the obvious strategy to use in determining it is first to measure the amount and the time independently then to combine the values the amount can be measured in terms of thickness or volume or mass per unit area the duration of the time interval can be preset using quasi continuous measurement techniques or site reoccupation or it can be identified from interval specific sedimentary structures or it can be measured using dated horizons an alternative strategy is to use a surrogate measurement variable rates of erosion in ancient systems are usually measured in this way using cosmogenic radionuclide concentrations these two strategies are reviewed in this paper sets of measurements made in systems that are active today can certainly be used to estimate the rate of sedimentation for the system as a whole this estimation is best carried out using geostatistical estimation techniques the alternative is simply to average the measured rate values this latter approach should not be used however because the mean sedimentation rate in a system gives information only about the net sediment movement at the system boundaries it says nothing at all about how the system is operating or about its spatial and temporal variability measurements of rates of sedimentation made for source to sink studies are necessarily made in stratigraphic successions the measurements are used to estimate quantities in the sediment mass budget equation the amount of decumulation is inherently incapable of being measured in stratigraphic successions therefore there are always unknowns in the mass budget equation whenever the lithic surface at the start of the time interval considered cannot be recognised everywhere this means that the mass budget equation is applicable in practice only when all the systems involved in the study are entirely non erosional for that entire time interval a highly unrealistic situation the consistently inverse relationship documented between accumulation rates and measurement timespan is taken usually to indicate that this relationship is substantially scale invariant this in turn is often taken as indicating that the stratigraphic record is fractal in nature there are nevertheless grounds for doubt all of which relate to the ways that the data are collected and used for estimation the relationship is in fact the natural mathematical result of last in first out lifo operation and is produced in any type of system in which addition and removal processes both operate it says nothing particular about sedimentation processes the future analysis of accumulation rate data collected from stratigraphic successions will sensibly be framed in the context of estimating the parameters of a lifo model

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

the middle eocene seeb formation of oman an investigation of acyclicity stratigraphic completeness and accumulation rates in shallow marine carbonate settings abstract the middle eocene seeb formation represents deposition on one of the earliest modern style carbonate platforms i e influenced by seagrasses and mangroves and presents an opportunity to explore controls on the preservation of cenozoic carbonate lithofacies in the study area the seeb fm is dominated by an anomalously thick approximately 250 m and uniform package of shallow marine platform interior sediments these nodular indistinctly bedded shallow subtidal sediments display no evidence for relative sea level change such as subaerial exposure features and lack the shallowing upwards cyclothems that have characterized carbonate sediments deposited in platform interior settings throughout much of the rock record particularly during greenhouse periods we conclude that this is a consequence of thorough bio retexturing of the sediment by burrowing organisms and the roots of marine vegetation which destroyed primary fabrics facies diversity evidence for cyclicity and missing time horizons such as cycle bounding exposure surfaces it seems possible that the remarkable thickness of apparently acyclic seeb fm sediment that built up may reflect increased bio disturbance of the shallow marine environment following the late cretaceous expansion of seagrasses and mangroves a similar lack of peritidal cyclothems may be common to many cenozoic shallow marine carbonate deposits missing time horizons in limestones reflecting erosion or nondeposition have been identified by some authors to explain discrepancies between low calculated accumulation rates of ancient sediments and higher rates measured in comparable modern environments however our studies of the seeb fm suggest that the significance of such missing time horizons in ancient sediments may have been overstated and that apparent differences between modern and ancient accumulation rates are a consequence of the extrapolation of unrepresentative localized high rates of modern sediment production to large platform scale areas our study reinforces the idea that modern sediment production and accumulation rates may be much lower than previously thought because they are typically measured in highly productive areas such as seagrass beds and do not take into account the highly variable nature of carbonate production storage erosion and destruction across platforms therefore far less missing time needs to be inferred for ancient sediments to account for any imbalance between modern and ancient sediment accumulation rates

uplift rate transients at subduction margins due to earthquake clustering coastal uplift is common in continental fore arc systems with elevated paleoshorelines indicating that uplift rates can vary dramatically over time on individual margins the origins of these changes in uplift rates are examined using a global data set of paleoshorelines together with 2 d numerical models of subduction systems empirical paleoshoreline data n 282 from eight subduction margins indicate that uplift rates are generally not steady state and varied by up to a factor of 20 during the late quaternary 125 ka on many subduction margins uplift rates increase to the present day a finding which we attribute to sampling bias toward those locations where holocene uplift rates have been highest with respect to other global margins which have undergone fast subsidence or no vertical motion e g a property akin to the so called sadler effect paleoshorelines and 2 d models suggest that transient uplift rates at subduction margins are mainly a short term 20 ka phenomenon that cannot be accounted for by plate boundary scale processes such as changes in the rates of plate convergence sediment underplating or isostatic unloading instead time variable uplift rates are ascribed to temporal clustering of large magnitude earthquakes on upper plate faults and to a lesser extent the subduction thrust the potential for future damaging earthquakes and tsunamis may have been underestimated at active subduction margins with no measureable holocene uplift and in such cases late quaternary paleoshorelines could provide an important constraint for hazard analysis

stochastic and deterministic controls on stratigraphic completeness and fidelity compilations of sedimentation rates determined across a large range of time spans and different sedimentary environments attest to the discontinuous nature of sedimentation and support the reasoning that hiatuses pervade sedimentary successions at multiple spatial and temporal scales the relationship between sedimentation rate and time span of observation also emphasises how stratigraphic completeness is a time span dependent concept the scaling of stratigraphic completeness with time span alludes to the likely stochastic and fractal nature of the stratigraphic record it also implies that the relationship between stratal thickness and time is inherently non linear and this has obvious implications for the way we should expect temporal processes to be recorded stratigraphically order within the stratigraphic record may arise from deterministic processes in stratigraphy most notably through astronomically influenced sedimentation intuitively a strongly ordered stratigraphic record due to the presence of cyclicity in sedimentation increases stratigraphic completeness at time spans equal to and longer than the time span of the cyclicity and minimises the non linearity between stratal thickness and time here geological data and simple modelling are used to support this supposition but these results also highlight how stochastic variability inherent in depositional processes may sensitise certain successions to missed cycles and incompleteness even in the presence of strong cyclicity this stochastic variability has the potential to mask evidence of astronomical forcing of sedimentation it is also shown how hiatuses affect the ability of a succession to faithfully record temporal processes and this is true regardless of whether hiatuses are deterministically controlled or random or indeed whether a succession is considered complete or not consequently stratigraphic completeness and stratigraphic fidelity are not synonymous terms

quantifying sediment transport dynamics on alluvial fans from spatial and temporal changes in grain size death valley california how information about sediment transport processes is transmitted to the sedimentary record remains a complex problem for the interpretation of fluvial stratigraphy alluvial fan deposits represent the condensed archive of sediment transport which is at least partly controlled by tectonics and climate for three coupled catchment fan systems in northern death valley california we measure grain size across 12 well preserved holocene and late pleistocene surfaces mapped in detail from field observations and remote sensing our results show that fan surfaces correlated to the late pleistocene are on average 30 50 coarser than active or holocene fan surfaces we adopt a self similar form of grain size distribution based on the observed stability of the ratio between mean grain size and standard deviation downstream using statistical analysis we show that fan surface grain size distributions are self similar we derive a relative mobility function using our self similar grain size distributions which describes the relative probability of a given grain size being transported we show that the largest mobile grain sizes are between 20 and 35mm a value that varies over time and is clearly lower in the holocene than in the pleistocene a change we suggest is due to a drier climate in the holocene these results support recent findings that alluvial fan sedimentology can record past environmental change and that these landscapes are potentially sensitive to climatic change over a glacial interglacial cycle we demonstrate that the self similarity methodology offers a means to explore changes in relative mobility of grain sizes from preserved fluvial deposits

inferring autogenically induced depositional discontinuities from observations on experimental deltaic shoreline trajectories palaeo shoreline is a commonly used proxy for palaeo sea level but only if deposition is continuous and constant will shoreline trajectory t l completely capture sea level time series e t artificial deltas were generated in the eurotank flume facility under stepwise tectonic subsidence periodic sea level fluctuation and two periodic water discharge scenarios one in phase and the other out of phase with sea level independent input variables tectonic subsidence y sea level e and water discharge q controlling sediment supply s were varied and dependent output variable shoreline trajectory twas monitored these experiments confirm that deposition is discontinuous even for continuous sediment supply and this hinders the inference of sea level curve from shoreline trajectory these results justify the here developed methodology for converting shoreline trajectory from the space domain to the time domain thereby improving the accuracy of the inferred sea level curve 2015 john wiley sons ltd

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

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

climatically controlled formation of river terraces in a tectonically active region along the southern piedmont of the tian shan nw china abstract combined tectonic uplift and quaternary climate variability control the deposition and abandonment of terraces along the southern tian shan in northwest china several preserved terraces have been deformed by an actively growing anticline within the uplifted frontal thrust system of the southern tian shan we combine geomorphic mapping topographic surveys of the deformed terrace surfaces 10be terrestrial cosmogenic nuclide tcn depth profile dating and optically stimulated luminescence osl dating to develop a new chronology for the terraces along the huangshui he since 550 ka our in situ 10be dating of fluvial gravels capping strath terraces suggests a relationship between the formation and abandonment of the terraces and glacial climate cycles since the middle late pleistocene these data indicate that the formation of the four terraces occurred at 550 430 350 and 60 ka we suggest that episodes of aggradation were facilitated by high sediment supply during glacial periods followed by subsequent incision that led to abandonment of these terraces during deglaciation we also estimate that tectonically induced river incision may account for about 60 70 of the total incision however during the intervening time between 350 ka and present only one terrace was formed and preserved we suggest that this record might be caused by a gradually decreasing uplift rate of the anticline through time and thus has influenced the preservation of terraces therefore our results demonstrate the utility of chronologic records from southern tian shan for deconvolving the effects of tectonics and climate on fluvial incision

the detection and illustration of regular sedimentary cycles using walsh power spectra and filtering with examples from the lias of switzerland power spectral analysis provides an objective method for the detection of regular cyclicity in data recording some oscillating parameter or time series digitization of measured stratigraphic sections is a convenient method for generating long time series during the examination of pelagic sequences for cyclicity related to orbital variations or milankovitch cycles the application of walsh power spectral analysis to stratigraphic sections is outlined and band pass filtering using the walsh transform introduced it is shown that variations in sedimentation rate hiatuses bioturbation and variations in compaction have the effect of damping or destroying spectral peaks the wavelength ratios of spectral peaks are often used during studies of milankovitch cycles to decide which orbital cycles are involved however in some circumstances hiatuses are able to alter wavelength ratios averaged walsh power spectra were generated for three liassic limestone shale sequences from breggia gorge switzerland the 21 000 year 21 ka precession cycle was detected in all three cases the 100 ka eccentricity cycle in two cases and the 41 ka obliquity cycle in one filtering revealed that the supposed 21 ka sedimentary cycles are grouped into packets of four or five small and large amplitude cycles the packets reflect the 100 ka modulation of the 21 ka precession cycle local disruption of the packaging can be used to locate hiatuses in pelagic strata

quantifying stratigraphic completeness a probabilistic approach using paleomagnetic data although sedimentary hiati of variable magnitude are abundant in most stratigraphic sections quantification of the degree of completeness for individual sections has proven difficult a new method of estimating stratigraphic completeness is developed for sections that preserve a detrital remanent magnetic reversal history because the timing of geomagnetic reversals is independent of sedimentation events the distribution of reversals in a stratigraphic section can be used to evaluate completeness the most direct method in which sections are sampled at the top and base of each stratigraphic unit evaluates the frequency of reversals within units versus at unit contacts the more complete a section the greater the probability that reversals occurred during depositional events and are recorded as within unit reversals the less complete a section the greater the probability that reversals occurred during depositional hiati and are recorded as unit contact reversals monte carlo simulations suggest that

the pulse of calm fan deltas abstract at the heart of interpreting the history of earth surface evolution preserved in the rock record is distinguishing environmental allogenic forcing from internally generated autogenic noise allogenic deposits classically have been recognized by their cyclic nature which apparently results from periodic changes in base level sediment supply or tectonics autogenic deposits which are quite variable in their origin and scale are caused by the nonlinearity of sediment transport and might be expected to have a random or scale free fractal signature here we describe a robust mechanism that generates cyclic deposits by an autogenic process in experimental fan deltas sheet flow over the fan surface induces deposition and an increase in fluvial slope and curvature to a point where the surface geometry is susceptible to a channelization instability similar to channel initiation on hillslopes channelized flow results in incision and degrading of the fan surface to a lower slope releasing a

box cores from the equatorial pacific 14c sedimentation rates and benthic mixing abstract carbon 14 determinations on box cores of calcareous ooze from the western and eastern equatorial pacific suggest that patterns of mixed layer ages sedimentation rates and mixed layer thicknesses are controlled by gradients of carbonate dissolution and fertility and by small scale redeposition processes mixed layer ages range from 3000 to 7000 years with a mode between 4000 and 5000 years sedimentation rates range from 0 8 to 2 4 cm 1000 years mixed layer depths calculated according to the box model of mixing range from 7 cm to 16 cm observed thicknesses are about one fourth smaller than calculated ones

stratigraphic completeness tiered trace fossils provide a measuring stick trace fossil associations commonly display a characteristic vertical zonation tiering within the substrate when burrows of a particular tier become truncated by turbidites tempestites or other results of catastrophic events they provide a simple but quantitative caliper for estimating stratigraphic incompleteness the minimum amount of penecontemporaneous sea floor erosion can be determined by types and sequences of trace fossils preserved below event deposits

twentieth century dune migration at the great sand dunes national park and preserve colorado relation to drought variability abstract the great sand dunes national park and preserve in southern colorado contains a large dune mass banked against the sangre de cristo mountains the dune mass is bounded for hundreds of kilometers by a vegetated low relief sand sheet with abundant active parabolic and barchanoid dunes the clear morphology of these dunes formed by winds mostly from the southwest and the unambiguous identification of these forms in remotely sensed images provide straightforward targets to assess temporal changes in dune position a digital database of georeferenced remote sensing images from 1936 to 1999 is used to quantify parabolic and barchan dune migration rates and surface reflectance an indicator of vegetation cover with evolving drought conditions in the twentieth century the total net migration of 13 parabolic dunes in 63 years is 0 31 to 0 66 km whereas 11 barchan dunes moved an average of 0 12 to 0 47 km compared to intervening wet year there is at least a three fold increase in average parabolic dune migration during well documented droughts in the 1930s 1950s and 1990s with a concomitant reduction in vegetation cover and surface water resources the landscape response to the most recent drought in the late twentieth century is documented by an average parabolic dune migration rate of 30 m year which is a six fold acceleration over prior wet years and similar to dune response during the 1930s a nonlinear threshold for parabolic dune migration is indicated with lower quartile palmer drought severity index values of