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

from quantitative 3d seismic stratigraphy to sequence stratigraphy insights into the vertical and lateral variability of shelf margin depositional systems at different stratigraphic orders abstract a major challenge in sequence stratigraphy is objectively identifying stratigraphic surfaces and sequences across multiple scales of observation identification is commonly dependent on the resolution of the data used i e seismic vs well data its dimension i e 1d vs 2d vs 3d or the criteria chosen to select sequence boundaries through shelf edge trajectory analysis the clinothem i e highest order seismic sequence identified on seismic data can constitute the elementary building block of an observation based and data driven quantitative workflow to develop sequence stratigraphic frameworks across different orders and ranks of hierarchy here we use high quality 3d seismic data to interpret a late tithonian early cretaceous shelf margin the lower barrow group lbg developed in the northern carnarvon basin on the north west shelf of australia based on full volume seismic interpretation techniques that integrate the 3d variability of the data when identifying seismic unconformities a high resolution seismic stratigraphic framework was built 73 interpreted clinothems with an average time duration of 63 000 yrs the computation of high frequency shelf edge trajectory angle tse curves on selected seismic cross sections is used to objectively pick sequence stratigraphic surfaces based on the accommodation succession method thereby highlighting small changes in trajectory and proposing a method reproducible by interpreters based on the same quantitative data within the d lobispinosum interval 142 3 140 9 ma the definition of stratigraphic sequences and composite stratigraphic sequences through this workflow is used to discriminate the controls at high and low temporal frequency on the vertical and lateral variability which is here quantified of this shelf slope basin system the results show that the high frequency interplay between short term glacio eustasy i e milankovitch eccentricity cycles of 100 000 yrs and sediment supply locus of fluvial input along the margin impacted the three dimensional stratigraphic architecture of the lbg in contrast tectonic subsidence had a significant impact on the stratigraphic architecture of the lbg within the main depocentre at lower temporal frequency by overprinting the eustatic signal and accelerating decelerating the rates of accommodation creation however identification of long term glacio eustatic milankovitch cycles 400 000 yrs outside the main depocentre where the rates of accommodation creation due to rift related subsidence are moderate also suggests low frequency eustatic control therefore the vertical and lateral variability of the lbg results from variations in sediment supply and subsidence regime under local i e process regime currents regional i e tectonics and global i e eustasy climate forcing parameters interplaying across timescales in contrast to standard sequence stratigraphic workflows that are based on model dependent choices to select sequence boundaries quantitative 3d seismic stratigraphy constitutes an improved method to interpret 3d seismic data in shelf margin depositional systems within a sequence stratigraphic framework which provides an observation based and model independent tool allowing the definition of stratigraphic sequences with results that are reproducible across multiple stratigraphers this work highlights the need for developing new sequence stratigraphic tools and methods that integrate the 4d variability of depositional systems and moves beyond the two dimensionality inherent to current sequence stratigraphic methods quantitative 3d seismic stratigraphy represents a first step towards the creation of 3d sequence stratigraphic workflows that could improve the prediction of stratigraphic patterns and facies relationships source reservoir seal distribution across shelf margins

critical porosity and elastic properties of microporous mixed carbonate siliciclastic rocks by integrating elastic property measurements and quantitative mineralogic and petrographic analyses of 45 mixed carbonate siliciclastic samples from two wells drilled in late cretaceous rock of the south provence basin southeast france we can 1 identify and quantify the parameters controlling elastic properties 2 demonstrate that micrite can be considered as a porous medium with a low critical porosity averaging 18 and 3 relate diagenetic transformations pore structure modifications and elastic property changes microporous carbonates with compact anhedral and euhedral microrhombic micrites display a steeper decrease in compressional and shear velocities with increasing porosity than do carbonate rocks with moldic intergranular or intercrystalline macroporosity the low value of critical porosity estimated in micrites 18 as well as the steep slopes of velocity porosity relationships at low porosity is believed to result from a pore network geometry characterized by very flat thin pores bounded by planar faces of micrite crystals cementation of microrhombic micrite steeply increases elastic moduli whereas dissolution processes significantly increase porosity with low variations of elastic moduli thus critical porosity concepts can help describe and model elastic properties of micritic microporous carbonate

rates of delta progradation during highstands consequences for timing of deposition in deep marine systems estimated times required for 24 modern river systems to form a shelf edge delta range from 8 5 ka to 116 5 ka depending on fluvial sediment supply delta width shelf volume and shelf transport rates these values indicate that transport of sand into deep marine systems is likely to be significant during third order highstands of relative sea level factors such as shelf transport dynamics may slow delta progradation while submarine canyons cutting the shelf may reduce the time before deep marine deposition occurs interpreting ancient sand rich deep marine strata as lowstand deposits without sufficient palaeogeographic information may not therefore always be appropriate

the petrophysical basis for shallow water flow prediction using multicomponent seismic data physical properties of shallow water flow swf sands differ from most reservoir and seal rocks studied for petroleum purposes these materials exist near the transition zone between rocks and sediments our investigations the subject of this article suggest that physical properties of swf sands are amenable to a prediction methodology that uses high resolution multicomponent seismic data swf sands are a primary hazard to deepwater drilling operations in the gulf of mexico they have the potential to result in well failures and significant discharges of subsurface fluids into the ocean however at present most operators make only a modest attempt to identify swf before drilling they drill through these hazards and mitigate any resulting damage at significant expense if one is encountered this is not rare according to a report from fugro geoservices approximately 70 of all deepwater wells have experienced swf a method for predrill delineation of sands that are close to failure and thus likely to exhibit swf would be advantageous in selecting optimal drilling locations and in developing cost effective well plans the current method of identifying swf involves predrill hazard studies utilizing conventional and high resolution seismic data to identify zones that might produce swf however the high incidence of swf mitigation events in deepwater wells shows that existing techniques do not provide adequate resolution or accuracy at present no robust seismic method exists for accurately identifying and characterizing swf operators do not have the option to avoid the hazard instead of mitigating the problem after it has started a new method is required that will permit operators to identify the hazard before the well is drilled using seismic data for accurate understanding of the physical properties and deformational behavior of swf sands is essential to characterization prediction and interpretation of these stratigraphic units to date very few core and

drowning of the mississippi delta due to insufficient sediment supply and global sea level rise global sea level rise reduced sediment supply and subsidence threaten the stability of the mississippi delta calculations of riverine sediment load and storage indicate that 10 000 13 500 km2 of the delta could be submerged by ad 2100

accommodation and supply a dual control on stratigraphic sequences abstract it is widely accepted that both eustatic and tectonically controlled regional changes of sea level have contributed to the record of stratigraphic sequences i suggest that environmental change be added as a third autonomous control sedimentologic principles clearly indicate that sequences and their systems tracts are controlled by the interplay of two rates the rate of change in accommodation space available for sedimentation and the rate of sediment supply sea level has direct control on accommodation but its influence on sediment supply is remote and easily overshadowed by environmental factors for instance the record of the most recent sea level rise is a transgressive systems tract where supply is low it is a prograding highstand systems tract in deltas where the supply is high examples of sequence boundaries generated by changes in sediment supply include tectonically driven shifts in sediment input into basins changes in ocean currents pulsating supply from failure of submarine slopes and drowning of carbonate platforms by environmental stress furthermore the stratigraphic sequences in fluviatile continental basins are physically removed from sea level induced changes in accommodation and must have formed by changes in the rate and pattern of supply subaerial exposure of marine sediments at the sequence boundary is a most important criterion for recognizing sea level cycles as opposed to supply cycles other criteria include downstepping of shelf breaks and characteristic patterns in the spacing of time lines within sequences some third order cycles ca 0 5 3 ma duration meet these criteria others do not cycle stacking patterns and the shifting facies belts on cratons indicate that many second and third order cycles lack pronounced exposure unconformities and represent gradual changes superimposed on more rapid shorter oscillations seismic data yield poor images of these gradational changes because they lack resolution seismic models of outcrops show that near the limits of resolution the seismic tool tends to portray rapid changes in facies and bed thickness i e lateral variations in supply as unconformities seismic unconformities do not necessarily correspond to unconformities in outcrop the succession of stratigraphic sequences is best considered a composite record of sea level and environmental change separating the various controls requires carefully planned experiments work on the oxygen isotope curve another proxy for sea level has set an example in this respect

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

out of our depth on the impossibility of fathoming eustasy from the stratigraphic record the evolution of a sedimentary basin s gross morphology depends upon 1 basement movement 2 sediment accumulation and compaction and 3 variations of eustasy with time thus if an accurate history of eustasy could be derived it would aid in our understanding of basin stratigraphy and help in the prediction of sediment geometry from described areas techniques which attempt to determine the magnitude of eustatic sea level excursions include the measurement of 1 the amount of sedimentary onlap onto the continental margins with and without the use of hypsometric curves 2 the thickness of marine sedimentary cycles and the elevation and distance between indicators of old strandlines 3 the perturbations on individual thermo tectonic subsidence curves and stacked crustal subsidence curves 4 the variations in deep ocean oxygen isotopes found in sediments and 5 the size of variables used in graphical and numerical simulations of basin fill in terms of tectonic behavior rates of sediment accumulation and eustasy which invert the problem to date a combination of the use of relative sea level charts derived from sediment onlap of the continental margin with dimensioning by oxygen isotopes responding to glacial events offers the best potential for relative tectono eustatic sea level curves but even this method can not produce a unique solution for absolute eustatic variations mathematical modelling shows that at best it is possible to obtain only the sum of tectonic basement subsidence and sea level variations from the above methods and at worst not even that simple a combination thus every proposed scheme to measure eustatic sea level excursions assumes some behavior for two of the three underlying processes tectonic movement of the basement sedimentary accumulation and eustatic sea level each scheme then determines the third process relative to the assumed model behavior of the other two it would seem that like king canute we cannot command the sea though we can still use undifferentiated relative tectono eustatic sea level curves to generate a family of solutions which are the product of a variety of absolute sea level curves and tectonic models each solution has then to be assessed in terms of geologic setting and the hypotheses it generates

reconstruction of palaeoinfiltration during the holocene using porewater data laxemar sweden abstract the interaction between fracture groundwater and crystalline rock matrix was explored by extracting the porewater residing today in the low permeability saturated rock matrix about 100 m below surface concentrations of the natural tracers cl 18 o 2 h in the porewater along a 11 m long profile from a water conducting fractured deformation zone into the intact rock matrix are the result of superimposed changes in the fracture groundwater composition the tracer profiles have evolved by diffusive exchange of the porewater in the rock matrix with groundwater flowing in fractures of high and low transmissivity since the retreat of the last weichselian glacier from the laxemar investigation area sweden numerical simulations indicate the necessity of a diachronic arrival of surface infiltration signals in the two fractures at the sampling location and of heterogeneous transport properties in the rock matrix as determined for the individual rock samples stringent conclusions regarding the palaeoinfiltration conditions can only be obtained when at least two tracers with independent source terms i e salinity and temperature moisture source are simulated simultaneously quantification of the porewater fracture groundwater interaction allows modification of the different evolutionary stages of the palaeoinfiltration conditions over holocene times most prominently this suggests the absence of any influence of brackish water from the yoldia sea and littornia sea in the area and the requirement for warmer climate precipitation from 8 ka to 4 5 ka bp coinciding with the holocene thermal maximum the ability to interpret the natural tracer profiles in accordance with independent geological hydrological and climatic constraints indicates that matrix diffusion in crystalline rocks is effective over decametres within timescales of 10 14 ka the impact of matrix diffusion on the fracture groundwater composition will become measurable over these timescales especially in low transmissivity fractures these data demonstrate that porewater indeed acts as an archive for palaeohydrologic variations although the resolution is still limited

quantitative sequence stratigraphy sequence stratigraphy based on wire line logs cores and outcrops is entering its fourth decade of mainstream usage in industry and academia the technique has proved to be an invaluable tool for improving stratigraphic analyses in both clastic and carbonate settings here we present a simple quantitative technique to support sequence stratigraphic interpretations in clastic shallow marine systems the technique uses two pieces of data that are readily available from every subsurface field or outcrop study 1 parasequence thickness t and 2 parasequence sandstone fraction sf the key assumptions are that parasequence thickness can be used as a proxy for accommodation at the time of deposition and parasequence sandstone fraction can be used as a proxy for sediment supply this means that quantitative proxies for rates of accommodation development and sediment supply can be acquired from wire line logs cores and outcrop data vertical trends in parasequence thickness divided by sandstone fraction t sf approximate trends expected in systems tracts for changes in ratios of rate of accommodation development to rate of sediment supply the technique termed tsf analysis can also be applied at lower order sequence and composite sequence scales it provides a quantitative and objective methodology for determining rank and order of sequence stratigraphic surfaces and units absolute t sf values can be used to determine shoreline stacked shoreline and shelf margin trajectories four case studies are presented which demonstrate the robustness of the technique across a range of different data sets implications and potential future applications of tsf analyses are discussed

dynamic topography and long term sea level variations there is no such thing as a stable continental platform abstract globally uniform i e eustatic sea level trends with time scales approaching 100 myr have been inferred from both seismic and backstripping stratigraphic analysis at a small set of geographic sites that are presumed to lie on stable continental platforms and passive continental margins characterized by simple thermal subsidence histories e g the new jersey margin the western african margin we demonstrate using mantle flow simulations based on high resolution seismic tomography that both the new jersey margin and the conjugate western african margin have been subject to orders of 100 m of dynamic i e flow induced topography change over the last 30 myr we also show that the changing pattern of downwelling mantle flow associated with plate subduction is a significant contributor to the background eustatic sea level trend which is also of order 100 m during the 30 myr time window therefore late cenozoic variations of dynamic topography on these passive margin sites are comparable to the eustatic sea level changes and can partially mask the latter furthermore even if the observed trend could be accurately corrected for local dynamic topography variation the residual eustatic signal does not merely reflect changes in mean spreading rates at mid ocean ridges we conclude that the observed long term sea level variations at so called stable sites cannot be interpreted as eustatic moreover previous analyses that have used long term sea level trends as a proxy for spreading rates and geochemical fluxes must be revisited

stratigraphic solution sets for determining the roles of sediment supply subsidence and sea level on transgressions and regressions although identifying unequivocally the cause of transgressions and regressions from the rock record can be difficult we can place limits on the possible combinations of sediment supply subsidence and sea level that could generate an observed stratigraphic sequence using simple geometric models that estimate maximum rates of change in the three controlling variables and combining these with other limits derived from field observations we can plot a solution set to define the most likely range of variations in these three primary controls on shoreline migration this approach shows the amount each controlling factor must change alone or in concert to account for the stratigraphy these quantitative values can be used to decide what is geologically reasonable and what is not although a unique solution may not be available we can calculate the required parameters for the observed shoreline migrations which provide a basis for informed interpretations

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

autostratigraphy a framework norm for genetic stratigraphy abstract autostratigraphy is the stratigraphy generated by large scale autogenic processes and needs to be heeded because of a current overreliance on allogenic controls in sequence stratigraphy key principles of autostratigraphy emerging from the theory of autoretreat and a new understanding of alluvial grade derive from the non equilibrium stratigraphic response i e the general lack of equilibrium configuration of depositional systems the non equilibrium behavior of fluvial deltas during times t of steady dynamic forcing leads to variable stratigraphic response that is the inevitable result of length d and time scaling particular to the depositional system rather than necessarily reflecting any sudden or unsteady change in the rate of allogenic forcing some abrupt breaks in the stratigraphic record are not necessarily associated with changes in allogenic conditions but can result from purely autogenic processes of the system when t is comparable to or longer than 1 the depositional system takes the non equilibrium large scale autogenic response 2 the superposition of autogenic and allogenic components of the forcing is prominently nonlinear and thus 3 sequence stratigraphic models that have been built on the assumption of equilibrium response are incorrect autostratigraphic analysis makes it possible to detect and identify complex autogenic responses and unsteady allogenic events in the stratigraphic record by quantifying a temporal change in the magnitude of d autostratigraphy thus functions as a norm for genetic stratigraphy

accommodation succession δa δs sequence stratigraphy observational method utility and insights into sequence boundary formation the future of sequence stratigraphy depends on stratigraphers making observations with a common method so that physical frameworks can be clearly separated from interpretations of driving mechanisms depositional sequence boundary selection is a well known controversy that could be resolved with objective recognition criteria accommodation succession sequence stratigraphy refines traditional methods using sedimentary facies facies associations vertical stacking stratal geometries and stratal terminations as the objective record of competing rates of accommodation change and sediment fill through time observations are placed in context of lateral transgression and regression and vertical aggradation and degradation movement of shoreline through time across multiple timescales in hierarchal stacks the repeating motif consists of a subaerial unconformity and its correlative subaqueous surface overlain in coastal settings by a basinward shift in coastal onlap and strata with progradational to aggradation stacking then retrogradation and aggradation progradation degradation stacking these stacking patterns are bounded by key surfaces recognized by stratal terminations and characteristic vertical successions of facies this pattern is independent of time duration or position on a sea level curve but incorporates data resolution regional extent and hierarchal stacking examples from multiple datasets show the utility and objectivity of the method and provide insights into sequence boundary formation

numerical modeling of falling stage topset aggradation implications for distinguishing between forced and unforced regressions in the geological record abstract distinguishing between forced and unforced regressive strata is important for identification of systems tracts prediction of sediment bypass and reconstruction of relative sea level histories conventional sequence stratigraphic models distinguish between forced and unforced regressive strata through the presence of aggradational topset no aggradation during forced regression and style of shoreline trajectory descending in forced regressive strata and flat to rising in unforced regressive strata however because present models contain implicit assumptions about sediment supply and the response of coastal plain and fluvial deposystems to falling and rising relative sea level it is probable that these two scenarios are an oversimplification of a more complex reality this work investigates how topset aggradation might develop during relative sea level fall using 1264 runs from a simple diffusional stratigraphic forward model topset aggradation is characterized for each model run by a topset foreset volume ratio t f ratio when topset strata are present the t f ratio is 0 when no topset strata are present the t f ratio is zero multiple two dimensional model runs 0 4 or 2 my duration and constant sediment supply and discharge rates representative of medium size river systems suggest that sediment transport rate may be a key control on topset aggradation modeling a range of sediment transport rates for amplitudes of relative sea level fall from 0 to 100 m shows that with relatively high rates of sediment transport multiple model runs create strata with t f ratios up to 0 08 conversely relatively low sediment transport rates lead to higher volumes of topset deposition reflected by t f ratios ranging from 0 10 to 0 37 however critically high sediment transport with no relative sea level fall leads to topset aggradation very similar to that resulting from low sediment transport and high amplitude relative sea level fall this is an example of non uniqueness showing that topset aggradation can occur during falling relative sea level as well as steady to rising relative sea level depending on rates of sediment transport this result has been tested and verified with different rates of relative sea level fall and with additional three dimensional model runs including runs in a different model the results suggest that backstripped shoreline trajectories are likely to be a more reliable method of distinguishing forced from unforced regression and that interpretation and prediction of sediment bypass history may be more complicated than current sequence stratigraphic models suggest

fluvial responses to climate and sea level change a review and look forward summary fluvial landforms and deposits provide one of the most readily studied quaternary continental records and alluvial strata represent an important component in most ancient continental interior and continental margin successions moreover studies of the long term dynamics of fluvial systems and their responses to external or allogenic controls can play important roles in research concerning both global change and sequence stratigraphy as well as in studies of the dynamic interactions between tectonic activity and surface processes these themes were energized in the final decades of the twentieth century and may become increasingly important in the first decades of this millennium this review paper provides a historical perspective on the development of ideas in the fields of geomorphology quaternary geology vs sedimentary geology and then summarizes key processes that operate to produce alluvial stratigraphic records over time scales of 103 106 years of particular interest are changes in discharge regimes sediment supply and sediment storage en route from source terrains to sedimentary basins as well as changes in sea level and the concept of accommodation late quaternary stratigraphic records from the loire france mississippi usa colorado texas usa and rhine meuse the netherlands rivers are used to illustrate the influences of climate change on continental interior rivers as well as the influence of interacting climate and sea level change on continental margin systems the paper concludes with a look forward to a bright future for studies of fluvial response to climate and sea level change at present empirical field based research on fluvial response to climate and sea level change lags behind a the global change community s understanding of the magnitude and frequency of climate and sea level change b the sequence stratigraphic community s desire to interpret climate and especially sea level change as forcing mechanisms and c the modelling community s ability to generate numerical and physical models of surface processes and their stratigraphic results a major challenge for the future is to catch up which will require the development of more detailed and sophisticated quaternary stratigraphic sedimentological and geochronological frameworks in a variety of continental interior and continental margin settings there is a particular need for studies that seek to document fluvial responses to allogenic forcing over both shorter 102 103 years and longer 104 106 years time scales than has commonly been the case to date as well as in larger river systems from source to sink studies of quaternary systems in depositional basin settings are especially critical because they can provide realistic analogues for interpretation of the pre quaternary rock record

investigating carbonate platform types multiple controls and a continuum of geometries abstract current classifications of carbonate platforms use depositional gradient as the main criterion for separating systems into two end member types ramps and flat topped platforms ftps however many examples do not conform to this simple classification to investigate why this is and to better understand probable controls on platform development we have used a series of 2d numerical forward model runs to investigate how sediment production diffusional sediment transport and other controls such as tectonic subsidence antecedent topography and relative sea level oscillation interact to determine platform geometry modeling results reaffirm that rates of down dip sediment transport relative to rates of autochthonous production are a critical factor in maintaining a ramp profile in stable cratonic settings under a constant rate of relative sea level rise type of carbonate production versus water depth curve for example euphotic versus oligophotic is not a significant control in our model cases both euphotic and oligophotic production profiles produce ftps when diffusion coefficients are low relative to production rates and ramps when diffusion coefficients are relatively high these results suggest a continuum of platform types ranging from transport dominated low gradient systems at one end of the spectrum to in situ accumulation dominated systems at the other a system may be transport dominated because high energy processes are able to break down and transport even bound sediment or because carbonate factories produce only sediment that is easily transportable under even low energy conditions time evolution is also probably important initially low gradient systems will in the absence of sufficiently high sediment transport rates tend to evolve towards high gradient flat topped steep margined platforms many observed or inferred platform geometries are therefore likely to be transient forms and this could complicate interpretation investigating how basin bathymetry and style of subsidence control platform geometry suggests that in transport dominated systems strata simply drape the underlying topography and that pre existing breaks of slope and differential fault subsidence are a stronger control on platform geometry in in situ accumulation dominated systems rotational subsidence tends to create transport dominated systems during rotation as the topographic gradient increases and transport rate increases and outpaces in situ production rate relative sea level oscillations tend to move the locus of sediment production laterally along any slope present on the platform distributing the sediment accumulation across the whole width of the platform suppressing progradation and steepening and so favoring development of low gradient systems based on all these results we suggest that a simple cutoff classification into ramp and flat topped platform types can still be useful in some circumstances but a more meaningful approach may be to describe and predict platform strata in terms of a multiple dimension platform parameter space containing a continuum of geometries controlled by sediment production sediment diffusion coefficient antecedent topography differential subsidence effects relative sea level oscillations and perhaps other as yet unappreciated controls

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

high resolution sequence stratigraphy and implications for cretaceous glacioeustasy of the late cretaceous gallup system new mexico u s a

towards a sequence stratigraphic solution set for autogenic processes and allogenic controls upper cretaceous strata book cliffs utah usa upper cretaceous strata exposed in the book cliffs of east central utah are widely used as an archetype for the sequence stratigraphy of marginal marine and shallow marine deposits their stratal architectures are classically interpreted in terms of accommodation controls that were external to the sediment routing system allogenic and that forced the formation of flooding surfaces sequence boundaries and parasequence and parasequence set stacking patterns processes internal to the sediment routing system autogenic and allogenic sediment supply controls provide alternatives that can plausibly explain aspects of the stratal architecture including the following 1 switching of wave dominated delta lobes expressed by the internal architecture of parasequences 2 river avulsion expressed by the internal architecture of multistorey fluvial sandbodies and related deposits 3 avulsion generated clustering of fluvial sandbodies in delta plain strata 4 autoretreat owing to increasing sediment storage on the delta plain as it lengthened during progradation expressed by progradational to aggradational stacking of parasequences 5 sediment supply control on the stacking of and sediment grain size fractionation within parasequence sets the various potential allogenic controls and autogenic processes are combined to form a sequence stratigraphic solution set this approach avoids anchoring of sequence stratigraphic interpretations on a specific control and acknowledges the non unique origin of stratal architectures

thick turbidite successions from supply dominated shelves during sea level highstand emphasis on the association between relative sea level lowstand and the formation of sandy deep water fans has tended to downplay the significance of high sediment supply and its potential to create deep water fans even during sea level highstands the lance fox hills lewis shelf margin in southern wyoming suggests that high supply was critical in causing the accretion of this moderately wide maastrichtian shelf margin at a minimum rate of 47 8 km m y and the generation of large sand rich fans during every shoreline regression across the shelf it is surprising that fans developed from shelf margin clinoforms that show systematically rising shelf edge trajectories proxy for rising relative sea level as well as from those that show flat trajectories stable to falling relative sea level however the latter producing more sediment bypass resulted in bigger and thicker fans whereas the former produced somewhat smaller and thinner fans we term the former highstand fans and suggest caution in using the lowstand model for high supply systems