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

a sedimentological and cyclostratigraphic evaluation of the completeness of the mississippian pennsylvanian mid carboniferous global stratotype section and point arrow canyon nevada usa the mississippian pennsylvanian global stratotype section and point gssp are hosted within a shallow water dominantly carbonate succession in the lower part of the bird spring formation at arrow canyon nevada usa the boundary is marked by the first appearance datum fad of the conodont declinognathodus noduliferus sensu lato it is shown that the boundary interval is punctuated by numerous subaerial hiatuses represented by palaeokarstic surfaces and palaeosols which divide strata at this location into fourth order glacio eustatic cycles a well developed palaeosol horizon occurs d noduliferus it also coincides with a very marked facies change and a second order shift in cycle stacking patterns these characteristics violate international commission on stratigraphy guidelines which state that gssps should be chosen in sections showing continuous sedimentation and lacking vertical facies changes at or near the boundary because the mid carboniferous is an icehouse interval cyclostratigraphy is a powerful tool for high resolution correlation a comparison of the cyclostratigraphy of mid carboniferous strata at arrow canyon and in northern england indicates that a large number of glacio eustatic sea level oscillations are not recorded at arrow canyon and that this section contains over 25 missed beats of milankovitch band duration equating to a hiatus of 1 ma

cryptic sequence boundaries in braided fluvial successions in braided fluvial deposits consisting of monotonous successions of sandstone or conglomerate it may be difficult to distinguish regionally significant bounding surfaces sequence boundaries from autogenic channel scour surfaces major surfaces may be characterized by erosional relief and draped by lag deposits but not all sequence boundaries show these characteristics other clues to the presence of a major surface are sharp changes in detrital composition shifts in regional palaeocurrent trends and evidence of early diagenesis of the sandstones immediately below the sequence boundary examples of these attributes of cryptic sequence boundaries are illustrated from three mesozoic units in the colorado plateau area of the united states in the chinle formation triassic near moab utah angular intraformational unconformities overlie sandstones showing evidence of early diagenesis in the castlegate sandstone upper cretaceous of east central utah a cryptic sequence boundary can be discriminated from other erosion surfaces by the evidence of detrital petrography and early diagenesis palaeocurrent data indicate changes in regional palaeoslope at two sequence boundaries within this unit evidence of early diagenesis is also present at a sequence boundary in the kayenta formation jurassic of westernmost colorado

sand flow cross strata in tidal sands of the lower greensand early cretaceous southern england abstract sand flow cross strata formed by the avalanching of sand down slip faces dominate the foresets of the shallow marine tidal sands in the lower greensand early cretaceous of southern england the sand flow cross strata dip steeply at angles between 20 and 32 occur in trough and tabular crossbeds ranging between 0 3 and 10 0 m in thickness and vary in style between tongue shape and tabular forms with various intermediate compound types narrow tongue shaped sand flow cross strata hitherto considered as characteristic of eolian crossbeds are widespread in these marine sands similar structures and textures are observed associated with sand flows on small experimental subaqueous dunes and dry talus slopes slow rates of bedform migration and locally increased rates of ediment supply to the slip face are considered prime factors controlling the formation of subaqueous tongue shaped sand flows swifter bedform migration and more uniform sediment supplies favor tabular sand flows discrimination between subaqueous and eolian cross beds cannot be made based on sand flow characteristics however the rare occurrence of grain fall laminae in subaqueous cross beds suggests that thick grain fall deposits provide a criterion for distinguishing eolian from subaqueous cross beds

sequence architecture of ancient rocky shorelines and their response to sea level change an early jurassic example from south wales uk the sea cliffs of ogmore by sea in glamorgan south wales expose a succession of early jurassic nearshore carbonates that drape rocky palaeoplatforms a sequence stratigraphic interpretation allows the recognition of four retrogradationally stacked parasequences the internal facies architecture of each of which is controlled by the bathymetry and geometry of the underlying shore platforms preserved facies are interpreted as representative of foreshore shoreface and offshore environments supratidal facies are absent but representative storm terrace clast assemblages are preserved in all lithofacies as a result of the cannibalization of the backshore during periods of shoreline retreat driven by sea level rise biostratigraphical calibration allows the reconstruction of sea level history and the correlation of regionally important flooding surfaces in the rhaetian sinemurian of southern britain with the position of the contemporary shoreline this suggests that platform incision in south wales occurred several million years before the onset of major deposition superseding deposits above ancient rock shore platforms may therefore not be representative of the environment in which coastal incision took place as one of the best examples of its kind the rockshore at ogmore acts as a deposystem model for ancient rocky shores worldwide

palaeomagnetic correlation and dating of plio pleistocene sediments at the southern margins of the north sea basin a series of discontinuous sediment sequences of plio pleistocene age occur onshore around the southern north sea margins notably in the east anglian region of britain intensive lithological and palaeontological analyses of these sediments have shown that they record both major and minor oscillations in climate sea level and environmental conditions however significant uncertainties exist regarding the absolute and relative chronostratigraphies of many of these sequences hindering understanding of the relative impacts of climatic eustatic and tectonic changes on the palaeogeographic development of the southern north sea basin here a number of key east anglian plio pleistocene sites are subjected to robust palaeomagnetic and mineralogical examination in order to determine those sediments which display reliable syn depositional magnetic polarities which are thus of use in ascribing a palaeomagnetically determined age from comparison with the geomagnetic polarity timescale gpts based on a range of palaeomagnetic and complementary mineralogical methods reliable palaeomagnetic directions were obtained from eight sites with reversed polarities displayed by sediments from three sites these polarity determinations can be used to infer absolute ages and test published between site correlations

characterization and interpretation of discontinuity surfaces in a jurassic ramp setting high atlas morocco discontinuity surfaces are widely recognized but often poorly understood features of epeiric carbonate settings in sedimentary systems these features often represent hiatus surfaces below biostratigraphic resolution and may represent a considerable portion of the time contained in the sediment record from an applied perspective discontinuities may represent horizontal flow barriers and result in reservoir compartmentalization here a total of 80 condensed surfaces s1 firmgrounds s2 and hardgrounds s3 from a jurassic middle and upper bajocian assoul formation ramp setting of the high atlas in morocco are carefully documented with respect to their morphology their secondary impregnation by fe and mn oxides and phosphates and their palaeoecological record a statistical frequency distribution of two surfaces of the s1 type 1 1 surfaces of the s2 type and 0 4 surfaces of the s3 type per 10 section metres is observed along a 220 m long carbonate succession based on two stratigraphically and spatially separated study windows and correlative sections the stratigraphic frequency distribution the lateral extent and the nature of facies change across discontinuities are documented in a quantitative manner specific features of the study site include the considerable stratigraphic thickness of the assoul formation and the conspicuous absence of subaerial exposure related features based on the data presented here firmground and hardground surfaces are best interpreted as maximum regression related features relative sea level lowstand results in a lowered wave base and wave orbitals and currents result in sea floor omission and lithification care must be taken to avoid overly simplistic interpretations as differences in bathymetry and carbonate facies result in marked changes in discontinuity characteristics in proximal distal transects the data shown here are of significance for those concerned with the interpretation of shoal water carbonate environments and are instrumental in the building of more realistic carbonate reservoir flow models

chemical features and isotopic composition of gaseous manifestations on vulcano island aeolian islands italy an interpretative model of fluid circulation abstract between 1987 and 1995 gases were sampled from various manifestations on vulcano island including various fumaroles at la fossa crater and baia di levante and diffuse soil gas emissions in several areas which are characterized by high c02 fluxes since the end of 1987 volcanic activity has increased considerably showing a marked rise in temperature 300 c in 1987 to 670 c in december 1992 and in output of steam from crater fumaroles in addition variations have been observed in the chemical and isotopic compositions of gases and thermal waters which can be attributed to an increased inflow of deeper fluids the isotopic composition of fumarolec steam seems to be the result of mixing processes between a positive endmember of deep origin d 10 15 18o 6 8 and two endmembers of meteoric origin with different oxygen shifts variations observed in the c02 isotopic composition suggest that all sampled manifestations are fed by a single deep source which may be magmatic such a source would be characterized by the 613cco2 values of high temperature fumaroles 13cco2 0 these values are noticeably more positive than those generally attributed to magmatic gases 13cco2 5 8 implying crustal contamination processes of the magma the observed decrease in 18oco2 values of the crater fumaroles from 20 in 1978 to between 12 and 15 in 1993 1994 was probably caused by two different processes the first is a reduction of the enrichment factor between c02 and h2o which is related to the increased temperature of the gases and the second is a mixing with more negative waters of meteoric origin finally c02 addition or removal processes caused by interactions between deep gases and shallow hydrothermal waters are likely to be responsible for the different chemical and isotopic compositions of gaseous emissions in the vulcano porto area and the crater fumaroles

how fast do marine invertebrates burrow abstract the burrowing of bivalves arthropods and echinoderms collected from tidal flats and shallow subtidal sediments of the ogeechee estuary georgia u s a was analyzed using time elapse x ray analysis of thin walled aquaria the rate of sediment intrusion was determined for each animal burrowing rates ranged between 0 01 and 0 15 cm 3 h for suspension feeding animals deposit feeding animals moved between 1 and 10 cm 3 of sand per hour approximately 10 to 100 times more sediment than the suspension feeders moved over similar times neoichnological experiments show that ten filter feeding individuals could take as long as 115 yr to churn a 1 m 2 plot of sediment by indexing the measured burrowing rates to realistic animal population densities ten such mobile deposit feeders as irregular echinoderms could bioturbate the same sediment in just 42 days under the maximum population densities modeled the animals could bioturbate the sediment plot in 61 min given the reported results qualitative interpretation of the rock record is possible highly burrowed examples of the skolithos ichnofacies reflect high population densities and at least seasonal time spans highly burrowed examples of the cruziana ichnofacies may represent moderate population densities and short time spans

where does the time go assessing the chronostratigraphic fidelity of sedimentary geological outcrops in the pliocene pleistocene red crag formation eastern england it is widely understood that earth9s stratigraphic record is an incomplete record of time but the implications that this has for interpreting sedimentary outcrop have received little attention here we consider how time is preserved at outcrop using the neogene quaternary red crag formation england the red crag formation hosts sedimentological and ichnological proxies that can be used to assess the time taken to accumulate outcrop expressions of strata as ancient depositional environments fluctuated between states of deposition erosion and stasis we use these to estimate how much time is preserved at outcrop scale and find that every outcrop provides only a vanishingly small window onto unanchored weeks to months within the 600 800 kyr of crag time much of the apparently missing time may be accounted for by the parts of the formation at subcrop rather than outcrop stratigraphic time has not been lost but is hidden the time completeness of the red crag formation at outcrop appears analogous to that recorded in much older rock units implying that direct comparison between strata of all ages is valid and that perceived stratigraphic incompleteness is an inconsequential barrier to viewing the outcrop sedimentary stratigraphic record as a truthful chronicle of earth history supplementary material further details of the regional geology and specific information on outcrops are available at https doi org 10 6084 m9 figshare c 4561001

pleistocene decalcification of late pliocene red crag shelly sands from walton on the naze england uppermost sands of the red crag at walton on the naze essex and elsewhere in east anglia have been decalcified to iron stained quartz sands in contrast lower sands are only minimally altered and contain aragonitic and calcitic shells aragonitic shells are slightly dissolved chalkified but calcitic shells are unaffected cementation is limited to an addition of iron oxides now mainly haematite which also coat carbonate grains abundant iron oxide fines in the upper decalcified sands were liberated from the coatings of shells shells that have since dissolved the diagenetic nature of the contact between decalcified upper and unaffected lower sands is evident where it transects cross bedding the contact is knife sharp even smoothly truncating large shells and is usually planar and subhorizontal shelly sands immediately beneath the boundary contain similar amounts of aragonitic material as do sands further below locally the decalcification boundary has been contorted by cryoturbation implying that carbonate dissolution was a pleistocene event decalcification probably occurred when the area was affected by permafrost lower sands were cemented by ice and protected from dissolution upper sands were above the ice table and subject to chemically aggressive waters during summer thaws decalcification is believed to have taken place during an episode of climate amelioration when downward retreat of the ice table accompanied replacement of tundra by boreal forest highly acidic and podzolic soils developed beneath which shell carbonate dissolved sharp based decalcified zones in lowestoft till and devensian deposits in other parts of england can also be attributed to dissolution associated with permafrost

numerical investigation of particle velocity distributions in aeolian sand transport particle velocity distribution in a blowing sand cloud is a reflection of saltation movement of many particles numerical analysis is performed for particle velocity distribution with a discrete particle model the probability distributions of resultant particle velocity in the impact entrainment process particle horizontal and vertical velocities at different heights and the vertical velocity of ascending particles are analyzed the probability distributions of resultant impact and lift off velocities of saltating particles can be expressed by a log normal function and that of impact angle comply with an exponential function the probability distribution of particle horizontal and vertical velocities at different heights shows a typical single peak pattern in the lower part of saltation layer the particle horizontal velocity distribution is positively skewed further analysis shows that the probability density function of the vertical velocity of ascending particles is similar to the right hand part of a normal distribution function and a general equation is acquired for the probability density function of non dimensional vertical velocity of ascending particles which is independent of diameter of saltating particles wind strength and height these distributions in the present numerical analysis are consistent with reported experimental results the present investigation is important for understanding the saltation state in wind blown sand movement c 2009 elsevier b v all rights reserved

morphodynamics of intertidal dunes a year long study at lifeboat station bank wells next the sea eastern england sand is driven clockwise by tidal currents round a diamond shaped sand shoal in the entrance to the harbour at wells next the sea a population of dune bedforms occupying the ebb dominated channel on the western side of the shoal was monitored for a year october 1975 to october 1976 in terms of shape height wavelength superimposed immature dunes movement and bedform composition individual dunes and the population of dunes as a whole changed in response to sediment transport on astronomical tidal scales varying from the semi diurnal to the equinoctial and in response to seasonal meteorological forcing most change occurred during the autumn and winter when strong winds and gales created surges which in some cases very significantly enhanced the sediment transport ue purely to the astronomical tide dune height was on average greatest during the winter when the sea temperature was low and least during the period of summer warmth dune height also varied substantially on a spring neap tidal scale an increase in height with the onset of many of the springs being followed by a gradual lowering dune wavelength showed little response to the springneap variation of sediment transport but decreased significantly between winter and summer varying degrees of time lag accompanied all changes in bedform characteristics in response to hydraulic change although individual dunes had surprisingly large lifespans and ebb directed excursions some change was noted m the composition and statistical attributes of the bedform population as the result of appearances and disappearances the more vigorous episodes of sediment transport created immature nascent dunes some of which grew large enough to become incorporated as new members into the population of mature forms internally the dunes were dominated by ebb oriented cross bedding complicated by a variety of intra set discontinuities commonly associated with mud drapes some recorded the smoothing of crests during tidal reversal and others the immobility of the bedform over a number of tidal cycles occasionally many other discontinuities expressed the capture of immature dunes by the main bedform within the duration of a single ebb tide because of the frequent perturbation of the astronomical tidal sediment transport by meterological events little order to the horizontal arrangement of discontinuities within the sets was detected in contrast to other reported cases

processes controlling the dynamics of compound sand waves in the north sea netherlands the understanding of the morphodynamics of harmonic bed forms on the seabed is essential for modeling marine sediment transport and coastal morphologic development previous research has mainly focused on the type and distribution of bed forms but areally extensive data and time series of seabed features are scarce multibeam and side scan sonar data from four expeditions reveal the contrasts between a coastal site with asymmetric and flattened three dimensional 3 d compound sand waves on a shoreface connected ridge and an offshore site with asymmetric and sharp crested 2 d compound sand waves migration rates of the coastal sand waves are 6 5 20 m yr 1 while migration rates of the offshore sand waves are 3 6 to 10 m yr 1 this contrasting morphology and dynamic behavior of compound sand waves at the two north sea sites is explained by differences in the relative importance of tidal currents and wave activity near the bed these new field data provide parameters and boundary conditions for sand transport models while the empirically derived behavior of sand waves may be used to validate sand transport and sand wave models 2005

pliocene climate and seasonality in north atlantic shelf seas this paper reviews north atlantic shelf seas palaeoclimate during the interval 4 3 ma prior to and incorporating the mid pliocene warm period ca 3 29 2 97 ma fossil assemblages and stable isotope data demonstrate northwards extension of subtropical faunas along the coast of the carolinas virginia yorktown and duplin formations relative to the present day suggesting a more vigorous florida current with reduced seasonality and warm water extending north of cape hatteras reconstructed annual range for virginia 12 30 c this interpretation supports conceptual models of increased meridional heat transport for the pliocene sea temperatures for florida lower pinecrest beds were similar to or slightly cooler than summers 25 27 c today and were probably influenced by seasonal upwelling of cold deep water reduced seasonality is also apparent in the coralline crag formation of the southern north sea with ostracods suggesting winter sea temperatures of 10 c modern 4 c however estimates from pliocene bivalves 3 6 16 6 c are similar to or cooler than the present day this mixed signal is problematic given warmer seas in the carolinas virginia and climate model and oceanographic data that show warmer seas in the mid pliocene eastern north atlantic this may be because the coralline crag formation was deposited prior to peak mid pliocene warmth

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

episodic sedimentation how normal is average how rare is rare does it matter where repeated sharp changes of sedimentation are inescapable periodic cycles are commonly invoked to preserve uniform orderly variations from some supposed norm the sedimentary record rarely reflects such uniformity however as sedimentologists have gradually realized magnitude versus frequency of processes has received little attention in sedimentology recurrence interval recovery time and preservation potential are critical factors for evaluating their significance for the sedimentary record large magnitude processes which represent positive deviations from the norm and are rare on the human time scale must be significant over geologic time everyday processes may have obliterated much of the evidence the sedimentological importance of rare events is difficult to assess because the record of such events may be very subtle this is especially true if a deposit has been thoroughly bioturbated or if the record of an event is simply an erosional surface it has now become possible to evaluate quantitatively ancient episodic sedimentation using modern process rates as well as refined biostratigraphic and isotopic dating i predict that such evaluation will necessitate revision of our favorite depositional models which have become so important for exploration as well as for research modified journal abstract

pollen and dinoflagellates from the red crag at walton on the naze essex evidence for a mild climatic phase during the early late pliocene of eastern england spot sampling of the red crag formation at walton on the naze essex walton cray has revealed a diverse record of dinoflagellates pollen and other palynomorphs pollen from a basal horizon is dominated by pinus but also contains high values of sciadopitys and a small but diverse component of deciduous mesothermal trees taxodium is more common at 2 m above the base of the red crag and may represent a different part of a climate cycle a mild to warm temperate climate is inferred for the walton assemblages and a correlation with the reuverian b pollen substage late pliocene 3 0 to 2 6 ma is demonstrated thereby constraining the timing of an important marine transgression in eastern england dinoflagellates from the basal horizon and from 2 m above the base of the red crag generally indi cate a restricted marine environment but outer neritic to oceanic dinoflagellates are occasionally pre sent and imply the penetration of more saline north atlantic water masses into the southern north sea basin mild to warm temperate conditions are indicated by the presence of several thermophilic species the walton assemblages have strong similarities with those of the mid pliocene coralline crag formation of eastern england but differ in the presence of bitectatodinium tepikiense which along with an apparently reduced species richness gives evidence of cooler conditions a number of thermophilic species at walton are not reported from younger pliocene deposits in eastern england perhaps reflecting a less equable climate after northern hemisphere cooling at 2 55 ma

a record of reversed polarity carried by the iron sulphide greigite in british early pleistocene sediments abstract palaeomagnetic measurements were made on samples extracted from a short sequence of early pleistocene estuarine clays now exposed in a sea cliff near sheringham on the north norfolk coast uk on the basis of earlier palynological work these clays had been ascribed a pastonian late tiglian age the clays show marked changes in colour from reddish brown at the top of the unit to blue grey in the middle and grey brown at the base the palaeomagnetic data vary in close association with these colour changes the top and basal brown clays show scattered normal directions of low intensity while the middle blue clays show strongly clustered reversed directions of much higher intensities some samples taken from the boundary between the middle blue and upper red clays show upon demagnetisation a normal overprint on a stable reversed polarity using high gradient magnetic extraction magnetic concentrates have been obtained from the strongly magnetic middle blue clays the presence of iron sulphide minerals in these concentrates was identified using energy dispersive x ray analysis during scanning electron microscopy more specifically x ray diffraction identifies greigite as the only detectable ferrimagnetic mineral in the magnetic concentrates rock magnetic measurements show clear qualitative differences in the magnetic mineralogies of the three clay subunits but absolute identification of the magnetic mineralogy of the weakly magnetic upper and basal brown clays has not yet been possible we interpret the sequence as a primary reversed polarity record this record is carried by the iron sulphide greigite as a chemical remanence acquired during syn depositional reduction of iron via the decomposition of organic material in these anoxic tidal clays subsequently the upper and basal subunits of the clay have been oxidised by permeation of groundwater from the adjacent coarse grained sediments most of the griegite in the oxidised margins of the clay has been altered as a result to a new less efficient magnetic recording material which thus carries a later scattered low intensity normal overprint

marine event beds and recolonization surfaces as revealed by trace fossil analysis turbidites and tempestites exhibit characteristic distributions of trace fossils to gain maximum advantage of the sedimentological and palaeoecological significance of these traces an attempt should be made to relate each trace to the associated colonization surface this approach allows traces initiated at the normal top of an event bed to be distinguished from traces that subsequently passed into the bed from a higher colonization level or were initiated on the eroded surface of the bed

the ichnogenus teichichnus seilacher 1955 the ichnotaxonomy of the phanerozoic trace fossil teichichnus seilacher 1955 is revised and its ethology producers and environmental affiliation are re evaluated newly studied material reveals that teichichnus is a sub vertical spreite burrow with an arcuate shape containing stacked laminae and a passively filled terminal causative burrow funnel like extension of the terminal causative burrow and wall ornamentation may occur high variation of burrow morphology is common and has resulted in the erection of 18 ichnospecies of which only four are herein regarded as valid teichichnus rectus t zigzag t patens and t duplex these ichnospecies are characterised by their overall burrow shape spreite morphology and more subordinate occurrence of branching and sculpture as recommended ichnotaxobases combined modes of feeding become evident including deposit and suspension feeding suggesting that teichichnus is a dwelling trace rather than a feeding trace aside from the classical interpretation of polychaetes as producers many features accord with an interpretation of dwelling echiurans and holothurians this interpretation may apply for many post palaeozoic t rectus and t zigzag whereas t duplex and partly t patens are likely produced by arthropods i e trilobites and crustaceans bivalves are also considered for producing teichichnus like traces teichichnus is a marine trace fossil with predominance in shallow marine environments low diversity and high density occurrences of teichichnus characterise marginal marine paralic environments with reduced salinity i e brackish water and oxygen i e dysoxia whereas in shoreface and offshore settings teichichnus occurs in association with many other ichnotaxa and in low density deep marine occurrences of teichichnus are comparably sparse and isolated records may indicate dysoxic bottom conditions

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

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