how to interpret understand and predict stratal geometries using stratal control spaces and stratal control space trajectories interpreting and predicting basin margin stratal geometries requires understanding of controls such as variations in supply and accommodation ideally based on independent quantitative evidence stratal control spaces are a new tool to analyze controls on strata a stratal control space is an area volume or perhaps a higher dimensional space defined by a range of values of the controlling processes subsidence sediment supply and eustasy a three dimensional stratal control volume with axes of subsidence sediment supply and eustatic rates of change can be populated with probabilities derived from analysis of time series of subsidence supply and eustasy these empirical or theoretical probabilities indicate the likelihood of occurrence of any particular combination of control rates defined by any point in the volume the stratal control volume can then be analyzed to determine which parts of the volume represent relative sea level fall and rise where in the volume particular stacking patterns will occur and how probable those stacking patterns are for outcrop and subsurface analysis using a stratal control area with eustasy and subsidence combined on a relative sea level axis allows similar analysis and may be preferable a stratal control trajectory is a history of supply and accommodation rates interpreted from outcrop or subsurface data or observed in analogue and numerical experiments and plotted as a series of linked points forming a trajectory through a stratal control space two theoretical and one actual outcrop example are presented to demonstrate how stratal control trajectories can be analyzed to determine which controls are dominant the accommodation supply trajectory range ratio astrr is a useful metric to characterize trajectory geometry trajectories with astrr 1 can be considered accommodation dominated and astrr 1 indicates a supply dominated trajectory calculating the range of stratal control probabilities along the trajectory indicates the probability of the rates of change of subsidence supply and eustasy required to form the interpreted stratal geometry both types of stratal control trajectory analyses can provide important additional understanding and prediction of how why and where stratal geometries form

novel 3d sequence stratigraphic numerical model for syn rift basins analysing architectural responses to eustasy sedimentation and tectonics syn rift clastic sedimentary systems preserve a complicated stratigraphic architecture that records the interplay of tectonics eustatic sea level and storage and routing of sediments previous conceptual models describe and explain changes in depositional stacking patterns along a fault segment however stacking patterns and the nature of key stratigraphic surfaces is challenging to predict accurately with conventional sequence stratigraphic models that do not consider the three dimensional interplay of subsidence sedimentation and eustasy we present a novel geometric 3d sequence stratigraphic model syn strat which applies temporally and spatially variable fault scale tectonic constraints to stratigraphic forward modelling as well as allowing flexibility in the other controls in time and space syn strat generates a 3d graphical surface that represents accommodation although the model has the capacity to model footwall variation here we present model results from the hangingwall of a normal fault with temporal and spatial dip and strike predictions made of stacking patterns and systems tracts for a given set of controls sensitivity tests are tied to the depositional architecture of field based examples from the loreto basin gulf of california and alkyonides basin gulf of corinth here the relative influence of major sedimentary controls different subsidence histories varying sedimentation distribution including along strike variation in stacking patterns are assessed and demonstrate the potential of syn strat for reducing subsurface uncertainties by resolving multiple scenarios in addition the model demonstrates the nature of diachroneity of key stratigraphic surfaces that can arise in syn rift settings which could be represented by a bypass surface sequence boundary or reservoir seal maximum flooding surface in the rock record enabling a quantitative assessment of these surfaces is critical for prospect analysis in hangingwall half graben fills where these surfaces are heavily relied upon for well correlations that are used for hydrocarbon volume and production rate predictions

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

shoreline autoretreat substantiated in flume experiments abstract under conditions of constant sediment supply s to the basin and a steady rate of rise a in relative sea level the autoretreat theory predicts that shorelines can retreat landwards at a relatively early stage of delta growth and attain an autobreak state after which the existing subaqueous slope begins to be starved of sediment and thereby lose its clear delta front configuration a numerical model based on this theory further suggests that shoreline migration depends on the inclination of basin s basement slope and subaqueous depositional slope and to a lesser degree on the inclination of subaerial depositional slope two dimensional flume experiments in which a miniature delta is subject to steady forcing a const 0 s const 0 were conducted to test the expectations of the autoretreat theory the experiments consisted of two different series of runs one was of modulation associated with a narrow range of the ratio of water discharge to sediment discharge q s the other was of q s modulation with kept nearly constant the q s ratio was mostly responsible for changes in but also affected to some extent all experimental runs substantiated the landward turnaround feature of shoreline accretion i e autoretreat and the geometrical break of the delta front shape during its retreat phase i e autobreak the obtained shoreline trajectories hold their geometrical patterns even after they were nondimensionalized in terms of the s a ratio a key hypothesis confirmed in the experiments is that a and s can never balance each other both of the experimental series brought some systematic change of shoreline trajectories but the variations of shoreline trajectory due to modulation were much more striking than those related to q s even these contrasting results are consistent with the numerical predictions the present experimental results support the applicability of the autoretreat concept to natural environments and help clarify the processes governing the regression and transgression of a shoreline on a constructional margin

stratigraphic sequences and their chronostratigraphic correlation abstract the exxon sequence models of posamentier and coworkers incorporate two concepts which i question they suggest that rivers grade to a bayline but evidence from modern major rivers indicates that they do not they also proposed that fluvial sedimentary accomodation space is generated by the seaward shift in equilibrium profiles during sea level fall but this is too simplistic a model based on the use of schematic continental margin configurations which do not incorporate real slope and relief data in most cases a fall in base level leads to deltaic progradation and upstream fluvial incision most coastal plain fluvial wedges result from two processes sea level rise with the drowning and filling of estuaries and active source area tectonism major tectonic events adjacent to foreland basins such as terrane collisions lead to the development of sequences of third order type duration approximately 1 15 m y changes in intraplate stress regimes resulting from changes in regional plate kinematics have a similar episodicity and can be shown to be responsible for some third order cycles on extensional continental margins examination of the chronostratigraphic basis of the mesozoic cenozoic cycle chart of haq and coworkers reveals internal inconsistencies and an unrealistic downplaying of the built in potential for error this chart is not an approved global standard and it should be used with extreme caution

upper plate magma poor rifted margins stratigraphic architecture and structural evolution abstract although it is generally accepted that many distal magma poor rifted margins are asymmetric and can be divided into lower and upper plate margins little is known about the details of how and when this asymmetry evolves and how upper and lower plate margins can be distinguished this is due to the fact that most papers focused on the so called lower plate margins while the upper plate margins remained less well understood mainly due to the lack of public accessible drill hole data the aim of this paper is to provide a first order description of the global architecture and stratigraphic evolution of an upper plate magma poor rifted margin in order to provide such a template we focused on 2 seismic sections the ion 1000 line east indian margin and the screech 2 line newfoundland margin and describe key km scale outcrops from the fossil european margin exposed in the western central alps all of which document classical upper plate margins based on these data we show that upper plate magma poor rifted margins can be characterized by a staircase type architecture with terraces t 1 t 2 t 3 and ramps r 1 r 2 that result as a consequence of an evolution through a coupling exhumation and breakup stage we also defined key stratigraphic levels that we try to link with the evolution of the margin which enables us to link the tectonic evolution with the creation of accommodation space and formation of the staircase architecture that characterizes the upper plate margin from these observations we develop a conceptual model for the evolution of upper plate margins and discuss the applicability of this model for different strain rates rates of subsidence and sedimentation rates

large scale architecture in non marine basins the response to the interplay between accommodation space and sediment supply sedimentary successions of non marine basins can be considered in terms of accommodation space and sedimentary supply changes changes in accommodation space controlling the large scale architecture of non marine basins are different in areas with high and low sedimentary supplies uplift of intrabasinal monoclines and anticlines reduced the available accommodation space resulting in changes in both the geometry of the depositional sequences and the large scale architecture of fluvial mudflat and shallow carbonate lacustrine deposits main drainage fluvial systems record areas with a high sedimentary supply while mudflats and shallow fluctuating lakes represent areas that received less sediment two end members in the large scale architecture of main drainage fluvial system in the almazan basin spain are i ribbon shaped channel fills with low interconnectivity which pass laterally into mudflats dominated by mudstones and evaporites and into palustrine and shallow carbonate lacustrine deposits mainly in the a2 depositional sequence and ii sheet like channel fills with high interconnectivity laterally correlated with stacked calcretes in the marginal mudflats in the upper part of a3 ribbon shaped channel fills formed in areas of high accommodation space and sheet like channel fills formed in areas of reduced accommodation space

experimental measurement of the relative importance of controls on shoreline migration abstract shoreline position in sedimentary rocks is a sensitive recorder of the interplay of several controlling factors the most important of these are thought to be the stratigraphic trinity eustatic sea level subsidence and sediment supply in ancient rock sequences it is generally difficult to disentangle the effects of these variables here we analyze the relative influence of sea level subsidence sediment supply and other controlling variables on shoreline migration in an experimental basin equipped with a subsiding floor the experiment used a linear hinge type subsidence profile for which the rate was kept constant in time constant overall sediment supply and base level variation on two time scales that were first applied separately and then superimposed although base level was the only controlling variable that was externally varied in time the base level changes induced changes in other variables indirectly e g by changing the partitioning of sediment between the fluvial and offshore segments of the system we examine the relative importance of measured direct and indirect changes in all the governing variables through the use of a moving boundary equation for shoreline migration when measured values are used for all the variables in the equation shoreline migration rate throughout the run can be predicted with a maximum r2 of 0 92 starting with this optimal prediction of the observed shoreline behavior we successively replace variables in the equation with their run averaged values degrading the prediction the relative loss of prediction accuracy as each variable is replaced is a measure of the importance of that variable in accounting for the observed shoreline migration by this measure base level is the most important variable followed in turn by sediment supply to the foreset geometry of the foreset and the average subsidence rate over the foreset from the shoreline migration equation we also derive a quantitative version of the a s ratio often applied in sequence stratigraphy the new formulation reduces to a form comparable to the traditional descriptive a s ratio if changes in foreset slope gain or loss of sediment to the fluvial system and spatial variation in subsidence rate are all negligible

a meta study of relationships between fluvial channel body stacking pattern and aggradation rate implications for sequence stratigraphy a quantitative comparison of 20 literature case studies of fluvial sedimentary successions tests common assumptions made in published models of alluvial architecture concerning 1 inverse proportionality between channel deposit density and floodplain aggradation rates and 2 resulting characteristics of channel body geometries and connectedness our results do not support the relationships predicted by established stratigraphy models the data suggest that channel body density geometry and stacking pattern are not reliable diagnostic indicators of rates of accommodation creation hence these architectural characteristics alone do not permit the definition of accommodation based systems tracts and settings and this calls into question current sequence stratigraphic practice in application to fluvial successions

autogenic attainment of large scale alluvial grade with steady sea level fall an analog tank flume experiment a graded river conveys its sediment load without net deposition or erosion the graded state is thought to represent the long term response of alluvial rivers to steady external forcing we show here that alluvial rivers building deltas can be in grade as an autogenic response to steady sea level fall consider an antecedent graded river profile the upstream end of which consists of an alluvial bedrock transition and the downstream end of which is a fixed overfall where constant sea level is maintained the antecedent graded profile is then drowned by a jump in sea level after which sea level drops the result is a new river profile ending in a prograding delta that deposits on top of the antecedent profile if the rate of sea level fall is constant and the length of the antecedent reach is sufficient the new profile eventually becomes parallel or quasi parallel to the antecedent profile maintaining grade as it progrades in the experiments reported here series of graded river profiles with prograding deltas are created by stacking fluviodeltaic systems each graded profile and its associated delta is stacked on its immediate predecessor for each fluviodeltaic system a graded alluvial profile is attained with any constant rate of sea level fall provided that the antecedent profile is of sufficient length experiments suggest that this autogenic approach to grade is more rapid for higher rates of sea level fall lower rates of sediment supply and higher water discharges

source to sink analysis of continental rift sedimentation triassic cuyo basin precordillera argentina abstract the northernmost outcrops of the triassic extensional cuyo basin in western argentina reveal a basal coarse conglomerate overlain by a thinning fining upward siliciclastic red bedded section with subordinated tuffs and microbial rich carbonates cerro puntudo formation unconformably covered by a second coarse conglomerate el relincho formation which were previously interpreted as two rifting events an integrated analysis of facies associations stacking patterns paleocurrent and provenance was carried out in order to reveal the rift sedimentation using a source to sink approach besides the traditional controls in continental basins e g sedimentation tectonics and climate this study considers possible drainage pattern evolution in order to differentiate isolated versus integrated depocenter stages u pb zircon data corroborate our analysis and reveal a volcanic basement source of 256 8 3 5 ma permian lopingian and a sedimentation age of 249 8 2 5 ma early triassic for a tuff interbedded within the cerro puntudo formation complementing previous age of 243 8 1 9 ma middle triassic at the top of this unit stratigraphic stacking allows the interpretation of three evolutionary stages a first stage represented by thick massive boulder volcanic rich conglomerates characterizing alluvial fan deposition indicates strong tectonic activity of border faults first rifting event these features suggest high surface gradient and high available space controlling accommodation and dispersal of gravity and debris flow deposits paleocurrents to the east reveal largely north south normal faults located to the west and sediment supply from a proximal volcanic source area a second stage represented by a notable fining thinning upward facies including fluvial and palustrine stromatolites with pedogenetic features deposits indicates a transition to tectonic quiescence these facies associations developed in a context of low sedimentation rate limited tectonic relief and low accommodation space a third stage is represented by greenish well rounded coarse grained polymictic conglomerates of el relincho formation that unconformably truncate the cerro puntudo formation these conglomerates are interpreted as perennial braided fluvial systems with paleocurrents to the northwest indicating drainage reorganization primarily influenced by climate change and combined tectonic reactivation previously considered the second rifting event climate change affected sediment delivery and allowed regionally connectivity and overfilling of the depocenters in this last stage northwest axial transport from variable sources within the precordillera to the southeast is inferred from provenance analysis indicating open linked depocenters this study suggests a new stratigraphic correlation for the northern part of the cuyo basin implying that during the first rifting event a semi arid climate prevailed with development of isolated and independent depocenters first and second stages whereas above the unconformity initiating the second rifting event third stage depocenters were interconnected in the light of our source to sink analysis such paleogeographic change allowed overfilling and laterally linkage of separate half grabens along the cuyo basin whereas tectonic reactivation may better explain renewed conglomerate deposition climate change toward more humid conditions allowed previously separated depocenters to be connected through axial drainages

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

principles of regression and transgression the nature of the interplay between accommodation and sediment supply the rate of change of accommodation at the shoreline a and the rate of sediment supply s are the primary factors controlling regression and transgression in the geological record or retreat and advance of a coastal depositional system the generally accepted notion here referred to as the a s ratio concept stating that the migration of a shoreline is controlled principally by the magnitude of the ratio of a to s is insufficient and somewhat misleading partly owing to the problem of dimensional confusion the interplay of a and s inevitably results in autoretreat of the shoreline whereby the seaward advance of any shoreline is halted and is subsequently turned to landward retreat provided there is a continuous rise of relative sea level how effective the autoretreat process is depends for a given period of relative sea level rising upon the length of potential time period for the seaward advance of shoreline and is proportional to a 2 s and a super 1 5 s super 0 5 in two and three dimensional sediment dispersal modes respectively autoretreat becomes more effective as a increases and or s decreases a functions more critically to the effectiveness than s does the a s ratio concept is only approximately applicable when autoretreat is less effective i e with very low a and or very high s in this sense the autoretreat theory and the a s ratio concept are complementary to each other the autoretreat mechanism is expected to be substantially useful not only in fluvial deltas but also in many other depositional systems e g barrier islands whose evolution has been considered in terms of the a s ratio concept

contributions to sequence stratigraphy from analogue and numerical experiments the sequence stratigraphic model although no longer focused on eustasy and accommodation has been until recently based largely on observation and interpretation of outcrop and subsurface data this approach may be restrictive if the current model places limits on what is observed and how observations are interpreted to make progress in our understanding of strata the sequence stratigraphic model and method should be tested against and fully incorporate theoretical and experimental results that provide new knowledge of 1 autogenesis 2 intrinsic stratigraphic responses 3 alluvial grade and 4 scales appropriate to single depositional systems evolving with relative sea level changes more extensive inclusion of analogue and numerical experimental results could lead to significant modification and refinement of existing sequence stratigraphic models

evolution of the rhone delta plain in the holocene abstract the delta plain of the rhone shows many sandy beach ridges cropping out at the surface we propose here a radiocarbon chronology for the accumulation of the sedimentary bodies and an interpretation of the morphology of the mouth lobes that they form morphologies of the lobes depend on four principal factors 1 the variation of the relative sea level which constitutes the morphogenic base level 2 the fluvial input volume of water discharge and sedimentary input number and position of the mouths 3 marine dynamics volume and direction of the longshore drift dominant wave direction 4 the accommodation space created by the rise of relative sea level along with the paleobathymetry onto which the lobe will prograde immediately in front of the delta and at sea our conclusions are the main holocene paleo delta lobes of ulmet and saint ferreol were contemporaneous being deposited from 4000 to 2000 yr bp however the fluvial style of their downstream channel meandering for ulmet channel and linear for saint ferreol and the lobe morphologies of both channels are contrasted rounded in the case of ulmet and elongated for saint ferreol the role of the accommodation space is confirmed by two recent drillholes traversing the entire holocene succession which reveal a prior stage of sedimentary filling in the case of the saint ferreol lobe thus limiting the accommodation space and favouring a rapid and pointed progradation of this lobe the decoupling between hydrological activity and progradation of lobe indicates the complexity of mechanisms in the large catchment basin of rhone however the high rate of progradation of saint ferreol lobe after 2900 bp is probably a consequence of the increase of human activity after this date the variation of relative sea level remains an important factor controlling the evolution of the rhone delta after 6000 bp the local stabilization of the relative sea level between 4585 bp and 3520 bp played an important role in the triggering of coastal progradation saint ferreol lobe eastern margin rhone delta

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

braided rivers within an arid alluvial plain example from the lower triassic western german basin recognition criteria and expression of stratigraphic cycles based on a detailed sedimentological analysis of lower triassic continental deposits in the western germanic sag basin i e the eastern part of the present day paris basin the conglomerat basal gres vosgien and conglomerat principal formations three main depositional environments were identified i braided rivers in an arid alluvial plain with some preserved aeolian dunes and very few floodplain deposits ii marginal erg i e braided rivers aeolian dunes and aeolian sand sheets and iii playa lake an ephemeral lake environment with fluvial and aeolian sediments most of the time aeolian deposits in arid environments that are dominated by fluvial systems are poorly preserved and particular attention should be paid to any sedimentological marker of aridity such as wind worn pebbles ventifacts sand drift surfaces and aeolian sand sheets in such arid continental environments stratigraphic surfaces of allocyclic origin correspond to bounding surfaces of regional extension elementary stratigraphic cycles i e the genetic units have been identified for the three main continental environments the fluvial type fluvial aeolian type and fluvial playa lake type at the time scale of tens to hundreds of thousands of years these high frequency cycles of climatic origin are controlled either by the groundwater level in the basin or by the fluvial siliciclastic sediment input supplied from the highland lower triassic deposits from the germanic basin are preserved mostly in endoreic basins the central part of the basin is arid but the rivers are supplied with water by precipitation falling on the remnants of the hercynian variscan appalachian mountains consequently a detailed study of alluvial plain facies provides indications of local climatic conditions in the place of deposition whereas fluvial systems only reflect climatic conditions of the upstream erosional catchments

the functioning of sediment routing systems using a mass balance approach example from the eocene of the southern pyrenees abstractsediment routing systems link source regions undergoing erosion with depositional sinks and involve a volumetric or mass budget understanding how these source to sink systems function is key to stratigraphic prediction but estimation of their surface sediment discharges and depositional fluxes on geological time scales is a challenging problem we recognize a paleosediment routing system from the geological record in the mid late eocene escanilla formation and time equivalents of the tectonically active wedge top region of the southern pyrenees by mapping the 200 km long fairway of the escanilla sediment routing system we obtain the sediment budget and grain size fractionation of three time intervals each of 2 5 2 6 m yr duration over the time period 41 6 33 9 ma four thousand cubic kilometers of sediment sourced principally from two feeder systems in the high pyrenees was deposited in a period of 7 7 m yr the positions of moving boundaries characterized by rapid reduction in the perc

shoal water deltas in high accommodation settings insights from the lacustrine valimi formation gulf of corinth greece the stratigraphic architecture of shoal water deltaic systems developed in low accommodation settings is relatively well known in contrast the features of shoal water deltas developed in high accommodation settings remain relatively poorly documented especially when compared with the available data sets for gilbert type deltaic systems developed in the same settings the lacustrine valimi formation gulf of corinth greece provides an opportunity to investigate the facies assemblage and architectural style of shoal water deltaic systems developed in high accommodation settings the studied interval accumulated during the pliocene and pleistocene and represents part of the early syn rift gulf of corinth succession six facies associations each described in terms of depositional processes and geometries have been identified and interpreted to represent a range of proximal to distal deltaic sub environments delta plain distributary channel mouth bar delta front prodelta and open lake the facies associations and their architectural elements reveal characteristics which are not common in traditionally described shoal water deltas of note different facies arrangements are observed in the distributary channels in different sectors of the delta passing from thick single storey channel fills embedded within delta plain fines in landward positions to thin amalgamated and multi storey channels closer to the river mouth this study proposes a new depositional model for shoal water deltas in high accommodation settings documenting for the first time that shoal water delta deposits can form a substantial part of stratigraphic successions that accumulate in these settings the proposed depositional model provides new criteria for the recognition and interpretation of these deposits the results of this study have applied significance for reservoir characterization

postglacial sea level rise and sedimentary response in the guadiana estuary portugal spain border abstract the study of sedimentological features foraminifera and molluscan fauna in samples recovered from four rotary boreholes permitted after 14 c dating the first assessment of the post glacial transgression in guadiana river estuary the holocene sequence is underlain by coarse sediments from delta fan enclosing continental swamp deposits dated 16 980 year bp the holocene sedimentary sequence was deposited either directly on this delta fan gravels or on top of fluvial sands deposited probably between 11 000 and 10 000 yr bp an accelerated phase of the estuary infilling by clayey sediments containing the salt marsh foraminifer trochammina began ca 9800 year bp when sea level was about 39 m below present between 7500 and 7000 year bp the central part of the estuary started to accommodate coarser sediments partially introduced from the continental shelf the first phase of holocene sea level rise at a rate of 0 85 m century terminated ca 6500 year bp since then lagoonal sediments in the vicinity of the estuary have been enclosed behind sand spits and predominantly sandy sedimentation was initiated within the estuary after a second phase of slower rise at the rate of 0 3 m century which lasted until ca 5000 year bp the sea approached the present level

three dimensional accommodation analysis of the keuper of the paris basin discrimination between tectonics eustasy and sediment supply in the stratigraphic record abstract during the keuper the paris basin was an intracratonic sedimentary basin filled by continental deposits using paleo environmental isopach and paleo altitude maps we estimate the variations of accommodation rate at the scale of stratigraphic minor hemi cycle 1 3 ma an analysis of the short and long wavelength accommodation variations allows us to assess the relative influence of tectonics eustasy and sediment supply on the stratigraphic record our data suggest a pattern of subsidence along three trends e w in the carnian e w to nne ssw in the norian and ne sw in the norian rhaetian during the keuper the paris basin accurately records the different phases of the opening of the tethys ocean associated with a rotation of the extension direction the norian cycle could thus reflect the intraplate stresses in a transitional period between the triassic and the liassic

how plausible are high frequency sediment supply driven cycles in the stratigraphic record abstract this paper is an attempt to quantify the plausible time scales of clastic sediment supply variations at the entrance of sedimentary basins our approach is based on the sedimentary system concept which simplifies natural systems by dividing them into three zones of dominant processes the erosion the transfer and the sedimentation subsystems we examine recent results from geomorphology which show that frequent climate changes can induce high frequency sediment flux variations at the outlet of the source area we put forward the crucial role of the transfer subsystem which conveys sediment from the erosion zone to the basin by applying a diffusive model to a number of worldwide rivers we extend from large 1000 km to intermediate 300 km rivers the previous finding that the transfer subsystem acts as a buffer for short periods sediment pulses tens to hundreds of kiloyears this implies that high frequency stratigraphic cycles in clastic accumulations fed by large drainage systems are unlikely to reflect sediment supply cycles of tens to hundreds of thousands of years of periodicities

a unifying framework for shoreline migration 1 multiscale shoreline evolution on sedimentary coasts 1 a unifying framework for shoreline migration is presented which synthesizes problems from coastal engineering geomorphology and stratigraphy into a common quantitative basis consideration of characteristic problems from these fields reveals that multiscale shoreline evolution problems naturally break into three classes on the basis of the morphologic unit of evolution shoreface bed versus shoreline planform versus stratigraphic shoreline trajectory shoreline evolution models correspondingly break into morphodynamic morphokinematic and hybrid approaches a generalized shoreline continuity equation is derived the shoreline exner equation which subsumes equilibrium profile models commonly used in geomorphology and engineering and provides a natural framework for interpreting shoreline trajectories preserved in the sedimentary record the shoreline exner equation provides a rigorous basis for geometric and moving boundary models which have significant untapped potential for shoreline migration problems recent advances in computational methods for evolving interface problems make hybrid models particularly attractive for problems of large scale planform shoreline dynamics such as delta evolution

the accommodation concept in sequence stratigraphy some dimensional problems and possible redefinition abstract a debate is provoked here as to what is meant exactly by the term accommodation and how well this concept as it presently stands serves the conceptual and quantitative framework of sequence stratigraphy accommodation in terms of its original definition contains some conceptual flaws it represents a space that has three dimensional extent associated with a certain availability of sediment and thus is not really independent of sedimentation however this space is fairly unspecifiable because of the inherent difficulty of distinguishing real accommodation from the space which is very unlikely to be filled by sediment anti accommodation the accommodation concept cannot be extended to subaerial environments because the equilibrium profile of streams which is sometimes used for this purpose is difficult to recognize even if it existed a possible redefinition of accommodation is suggested as the thickness measured at a specified site and time of a space which becomes filled with sediments during a specified time interval this accommodation is not a space but the thickness of a space not something potential but an objective result not specifiable from the graded profile or geomorphic base level but from stratigraphic base level and not separated from sedimentation but partly dependent from it potential accommodation may be used to describe the maximum of possible accommodation at a specified site and time which can substantially coincide with the height of a water column at a given site and time

large scale fluvial grade as a nonequilibrium state in linked depositional systems theory and experiment 1 a graded river conveys its sediment load without net aggradation or degradation grade is thought to represent the equilibrium state of a river system subject to steady allogenic forcing we address the concept of grade in linked depositional systems through a combination of mathematical modeling and flume experiments we develop a moving boundary morphodynamic model of fluviodeltaic sedimentation and use it to quantify the conditions necessary for a state of sustained grade in an alluvial deltaic system developing on a uniformly sloping shelf to test our theory we conducted a series of flume experiments in which we constructed laboratory scale fluviodeltaic systems under specific relative sea level histories on large spatiotemporal scales our theoretical and experimental results suggest an alternative view of grade as an intrinsically nonequilibrium state that requires a fall in relative sea level under conditions of stillstand or rise in relative sea level the equilibrium graded profile does not exist and the alluvial river will always aggrade with a steady sediment supply alluvial grade can be sustained if relative sea level falls with a specific square root of time dependence common sequence stratigraphic conceptualizations of alluvial river response to sea level change suggest that rivers aggrade and degrade in response to relative sea level rise and fall respectively we show that rivers can remain aggradational if the rate of sea level fall is sufficiently small the boundary between aggradational and degradational states is the graded state described here that associated with a relative sea level fall that varies with the square root of time

mass balance constraints on stratigraphic interpretation of linked alluvial coastal shelfal deposits from source to sink example from cretaceous western interior basin utah and colorado u s a abstract experimental work suggests that the rate of upstream to downstream loss of sediment from an active depositional system to permanent storage exerts a fundamental control on stratigraphic architecture this rate of sediment mass loss is determined by the spatial distribution of tectonic subsidence and rate of sediment supply the character of input sediment grain size distribution and composition is the third parameter that affects stratigraphic architecture we apply this concept in a mass balance framework to linked alluvial coastal shelfal deposits of the upper cretaceous castlegate sandstone blackhawk formation star point sandstone and mancos shale western interior basin utah and colorado usa facies partitioning and sediment budgets are estimated for eight stratigraphic intervals in order to compare temporal dynamics of the sediment routing system from erosional source to depositional sink mapping of each stratigraphic interval and its constituent segments from upsystem to downsystem was achieved along a representative dip oriented 2d cross section over a distance of c 350 km using extensive outcrop exposure and densely spaced subsurface wells the cross section provides time averaged estimates of the spatial distribution of deposition grain size data show that there is limited downsystem fining of any particular facies within the castlegate sandstone but that the proportion of facies changes systematically downsystem to accommodate an overall fining trend therefore it is reasonable as a first approximation to use facies proportions as a textural replacement for grain size sediment supply characteristics for each of the eight stratigraphic intervals are constrained by total facies proportions in each interval for each stratigraphic interval we assess the level of interaction between alluvial and coastal to shelfal segments of the routing system comparison of the downsystem mass balance characteristics of the eight stratigraphic intervals suggests that there were depositional gains and losses of shallow marine shale in the five youngest intervals which can be attributed to along strike sediment transport this result is consistent with increased interaction through time with vigorous wave and tide driven circulation in the seaway as the sediment routing system advanced out of a sheltered embayment in response to decreasing tectonic subsidence in the youngest stratigraphic interval the upstream unconformable base of the castlegate sandstone is marked by a pronounced increase in the sand to gravel grade mass fraction of the fluvially supplied depositional volume this marked increase can be attributed to hinterland unroofing and or cannibalization of wedge top basins leading to import of coarse grained sediment into the castlegate fluvial system our results demonstrate the value of analyzing downsystem sediment loss i e downsystem mass extraction within a mass balance framework as a simple and practical tool to quantify the relationship between accommodation and sediment supply and thus to decode past external forcing mechanisms from stratigraphic architecture

lower triassic sequence stratigraphy of the western part of the germanic basin west of black forest fluvial system evolution through time and space abstract the aim of this paper is to analyse the fluvial evolution of the lower triassic in the western part of the germanic basin through time and space as well as the impact of the geodynamic and climatic setting on the preservation of fluvial deposits the lower triassic crops out only in the vosges massif and the black forest so well log studies are required to realise sequence stratigraphy correlations and establish comparisons with others parts of the germanic basin in a first step we use well log data analyses to characterise the electrofacies associations in the triassic and then define the well log signatures of each formation in a second step the characterisation and recognition of genetic sequences and their stacking pattern allow us to define seven minor cycles integrated into two major cycles finally the quantification of the lithologies at different stages of basin evolution leads to the reconstruction of paleoenvironmental maps to illustrate facies evolution through space and time a comparison with cycles defined in the germanic basin allows us to propose correlations of the lower triassic on either side of the rhine graben and leads to a discussion of the evolution of fluvial systems through time and space during the scythian the fluvial style is characterised by braided fluvial systems evolving laterally into lake deposits towards the central part of the germanic basin during this stage the basin was a huge depression with very few marine connections in its extreme eastern part the stratigraphic cycles represent rhythmic fluctuations in relative lake level that could be attributed to sediment supply and or lake level variations in an arid setting four minor stratigraphic cycles are observed that are integrated within a single major stratigraphic cycle during the period of the stratigraphic base level rise of the major cycle a maximum of 233 m of sediment would represent a duration of sedimentation in the paris basin of at least 1 8 m y during the period of the stratigraphic base level fall of the major cycle a maximum of 65 m of sediment would have accumulated over 2 5 m y on the western edge of the germanic basin the top of the scythian is marked by a major sedimentary break characterised by a planation surface with preservation of the first paleosols followed by the hardegsen unconformity this unconformity is tectonically deformed leading to the development of a new sedimentation area in the west of the basin the fluvial sedimentation above this discontinuity shows a trend towards enhanced development of floodplain or lacustrine type environments at its western margin with the formation of paleosols the fluvial systems are linked with sabkhas and then with a shallow sea connected to the tethys ocean in this context the stratigraphic cycles are caused by variations in relative sea level and or sediment supply the fluvial deposits are preserved in an exoreic basin

static liquefaction of very loose sands discussion the study presented in this paper has provided further evidence to indicate that natural sands particularly those con taining fines or shells do not behave in the same way as clean sands however one of the conclusions made by the authors that is that the resistance to liquefaction increases with the effective confining stress may need further discus sion it is a common observation for a number of sands that the liquefaction behaviour of very loose sand is very sensitive to the void ratio after consolidation i e before undrained shearing figure d1 presents the effective stress paths of two undrained tests on loose sand cu3 and cu6 conducted under the same effective confining stress but on specimens with different post consolidation void ratios ec the ec for test cu3 is 0 962 and for test cu6 is 1 023 the difference in void ratios is only 0 061 however liquefaction occurs in test cu6 but not in test cu3 as seen in fig d1 the sand used is a granular fill material dredged from the sea it has a mean grain diameter of 0 3 mm it contains very little fines 0 4 but a high shell content of 14 one more example is given in fig d2 in which the results of two undrained tests on loose sand are compared the ec values of the two tests are 0 838 for test 6 and 0 849 for test 7 the difference in void ratios is 0 011 with this small difference in ec test 7 exhibits steady state behaviour and test 6 limit steady behaviour the basic properties of the sand used can be found in chu 1995 it can be seen from fig 5 for nevada sand and fig 7 for ottawa sand of the discussed paper that the e c value of each test at different confining stress is different and the higher the confining stress the smaller the e c the maximum difference in e c in these tests is 0 038 if the authors were to compare the liquefaction behaviour for tests with the same or nearly the same e c value the conclusion that the resistance to liquefaction increases with effective confining stress may have been different it should be pointed that it is the post consolidation void ratio e c that is used to establish the steady state behaviour i e castro 1969

heat flow heat production and granite depth in western france newly measured heat flow and full heat production determinations over the armorican massif western france are tested against a linear relationship as proposed through birch s law the data do not fit a strict linear relationship but are within an elongated cluster which can be approximated in mw m and km by these parameters are compared with those of surrounding hercynian regions data from the central massif and previously failed to fit any linear relationship data for scotland and southern england could not be fitted to a single line however the present data and those from southern and central england do fit a single line suggesting that the three regions form a single geothermal province the depth parameter is greater than the root depths of the granitic plutons indicating that heat sources can exist at depths below the granitic intrusions the deep crustal structure revealed from seismic studies agrees with the radiogenic elements distribution deduced from thermal data

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

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

estimation of the paleoflux of terrestrial derived solids across ancient basin margins using the stratigraphic record a simple inversion scheme for estimating sediment flux from ancient shelf margin successions is presented here by treating shelf margin clinothems as the product of deposition associated with migration of a shelf edge clinoform with constant shape at a rate equal to the shelf margin progradation rate assuming sediment conservation deposition can be broken into components of 1 response to subsidence and sea level changes and 2 basinward migration of the clinoform profile sediment flux can therefore be estimated with knowledge of progradation rate subsidence sea level change rate and clinoform dimensions an advantage of this methodology is that it requires only two dimensional data i e dip oriented cross sections rather than three dimensional volumes making it ideal for use with sparse data sets as well as with outcrops this methodology is also useful for analyzing areally limited data sets because it can predict the flux of sediment transported beyond the area of data coverage the approach is able to accurately reproduce the sediment flux estimates of previous workers from several margins the fox hills lewis zambezi new jersey and north slope margins using both volumetric and forward modeling methods not only are the predicted distributions for sediment flux across ancient shelf margins similar to distributions predicted by more data intensive theoretical models the estimated magnitudes for paleofluxes favorably compare with measured loads from modern rivers growth of continents is achieved in part by accretion of sediment on shelf margins the rates and patterns of continental expansion are therefore partially dependent on the magnitude and distribution of mass transfer from eroding hinterlands to continental margins fluxes which also play a critical role in global biogeochemical cycles flux estimates cast into a mass balance framework suggest that approximately two thirds of continental margin sediments are exported past the shelf edge into deeper water at long term geologic time scales this finding implies that two thirds of the terrestrial derived particulate organic carbon poc delivered from rivers to the ocean can be stored in deep water over geologic time scales the observations presented here indicate that repetitive delivery of sediment to margins by shelf edge deltas is fundamental to the long term process of margin accretion

allogenic controls on the fluvial architecture and fossil preservation of the upper triassic ischigualasto formation nw argentina abstract the upper triassic ischigualasto formation in nw argentina was deposited in a fluvial system during the synrift filling of the extensional ischigualasto villa union basin the expansive exposures of the fluvial architecture and paleosols provide a framework to reconstruct the paleoenvironmental evolution of this basin during the upper triassic using continental sequence stratigraphy the ischigualasto formation deposition can be divided into seven sequential sedimentary stages the 1 bypass stage 2 confined low accommodation stage 3 confined high accommodation stage 4 unstable accommodation stage 5 unconfined high accommodation stage 6 unconfined low accommodation stage and finally 7 unconfined high accommodation stage the sedimentary evolution of the ischigualasto formation was driven by different allogenic controls such as rises and falls in lake levels local tectonism subsidence volcanism and climate which also produced modifications of the equilibrium profile of the fluvial systems all of these factors result in different accommodations in central and flank areas of the basin which led to different architectural configurations of channels and floodplains allogenic processes affected not only the sequence stratigraphy of the basin but also the vertebrate and plant taphocenosis therefore the sequence stratigraphy can be used not only as a predictive tool related to fossil occurrence but also to understand the taphonomic history of the basin at each temporal interval

differential features of alluvial fans controlled by tectonic or eustatic accommodation space examples from the betic cordillera spain abstract the creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area along basin margin faults or to a rise in base level depending amongst others on the relative importance of these two factors the margins of terrestrial sedimentary basins where alluvial fans develop produce aggradational progradational or retrogradational stratigraphic architecture we studied a total of 43 quaternary alluvial fans in the granada and bajo segura basins betic cordillera spain the analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns which is the result of differences in eustasy and tectonics the qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related in each case to the main mechanism operative in the creation of accommodation space these patterns are described as follows 1 alluvial aggradation is the main result of high tectonic subsidence with the development of quite open but small fans with a constant steep slope lacking incised channels and headward eroding gullies 2 in contrast when the principal mechanism in creating accommodation space is low tectonic subsidence progradation occurs and the fans are narrower and larger moreover the slopes of such fans are less steep in relation to the drainage area than in the above case being constant or even concave in longitudinal profile they also have short deep incised channels culminating downfan in a depositional lobe in inactive zones long deep headward eroding gullies develop 3 areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin although with a pronounced mountain embayment which gives them a characteristic mushroom shape in plan view in the latter case retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas usually showing a segmented longitudinal profile with a low gradient the feeder channels do not surpass stream order 3 and various extremely long and shallow incised channels can appear 4 contrary to the case of fans developing under a regime of subsidence when the accommodation is due to base level rise the fan slopes bear no relation to the extent of the catchment basins in such a case the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet flows over the alluvial surface

mio pliocene to pleistocene paleotopographic evolution of brittany france from a sequence stratigraphic analysis relative influence of tectonics and climate the mio pliocene in western europe is a period of major climatic and tectonic change with important topographic consequences the aim of this paper is to reconstruct these topographic changes based on sedimentological analysis and sequence stratigraphy for the armorican massif western france and to discuss their significance the mio pliocene sands of the armorican massif red sands are mainly preserved in paleovalleys and are characterized by extensive fluvial sheetflood deposits with low preservation and by pass facies this sedimentological study shows that the red sands correspond to three main sedimentary environments fluvial alluvial fan low sinuosity rivers and braided rivers estuarine and some rare open marine deposits marine bioclastic sands faluns of french authors two orders of sequences have been correlated across brittany with one or two minor a s cycles comprised within the retrogradational trend of a major cycle the unconformity at the base of the lower cycle is more marked than the unconformity observed at the top which corresponds to a re incision of the paleovalley network a comparison of the results of the sequence stratigraphy analysis with eustatic variations and tectonic events during the mio pliocene allows 1 to discuss their influence on the evolution of the armorican massif and 2 to compare the stratigraphic record with other west european basins the unconformity observed at the base of the first minor cycle may be attributed to serravallian tortonian tectonic activity and or eustatic fall and the unconformity of the second minor cycle may be attributed to late tortonian early messinian tectonic activity the earlier unconformity is coeval with the development of a smooth paleovalley network compared to the jagged present day relief a single episode of mio pliocene deformation recorded in brittany may be dated as zanclean thus explaining the lack of the maximum flooding surface except in isolated areas from this study five paleogeographic maps were drawn up also indicating paleocurrent directions three maps for the lower cycle tortonian retrogradational trend late tortonian to early messinian maximum flooding surface and messinian progradational trend and two for the upper cycle pliocene retrogradational trend and piacenzian maximum flooding surface these maps show 1 the variations of paleocurrent directions during the mio pliocene 2 the extent of estuarine environments during the maximum flooding intervals and 3 a paleodrainage watershed oriented nnw sse following the regional quessoy nort sur erdre fault during the retrogradational trend of the upper cycle and possibly during the progradational trend of the lower cycle the present day morphology of the armorican massif is characterized by 1 incised