accommodation and sediment supply controls on clastic parasequences a meta analysis this study combines data from many published case studies to undertake a quantitative characterization of clastic parasequences with the aim to determine how accommodation sediment supply and autogenic sediment storage dynamics are recorded in their sedimentary architecture and stacking patterns results of this study are used to critically evaluate the validity of paradigms and models that are routinely used to explain and predict trends in the anatomy and arrangement of parasequences data on 957 parasequences from 62 case studies of clastic shallow water successions were coded in a relational database which includes outcrop and subsurface datasets of ancient and quaternary examples these units cover the preserved records of both river dominated deltas and wave dominated coasts representing shoreline transits over a breadth of timescales likely of both local and regional extent the role of extant accommodation rates of creation of accommodation and rates of sediment supply in determining parasequence architecture is assessed through analysis of relationships between i proxies of these variables at different scales rates of aggradation and progradation facies belt shoreline trajectories systems tract type parasequence set stacking patterns parasequence progradation angle and stratigraphic rise size of feeder rivers and ii parameters that describe the geometry and stacking style of parasequences and associated shallow water sand bodies statistical analyses of database outputs indicate which proxies of accommodation sediment supply and accommodation sediment supply ratio are significant as predictors of parasequence architecture and allow for interpretations of the importance of allogenic and autogenic factors the principal results of this study reveal the following i parasequence thickness varies as a function of water depth accommodation generation and erosional truncation and these variations are also reflected across types of systems tracts and parasequence sets ii the dip length of parasequence sand bodies demonstrates scaling with measures of accommodation sediment supply ratio at multiple scales partly in relation to the possible effect of sediment supply on progradation rates iii in systems tracts stratigraphic trends in parasequence stacking due to autogenic mechanisms or to acceleration or deceleration in relative sea level fluctuations are not revealed quantitatively iv some association is seen between the abundance of deltaic or river dominated parasequences and progradational stacking v positive but modest correlation is observed between measures of river system size and the dip length of shallow marine parasequence sand bodies the resulting insights can be applied to guide sequence stratigraphic interpretations of the rock record and the characterization of sub seismic stratigraphic architectures of subsurface successions

active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea shallow seismic profiles and borehole data revealed active moribund and buried tidal sand ridges in the east china sea and the southern yellow sea the ridges consist of relatively clean well sorted sands with fairly uniform sequences the microfossil assemblage exhibits a high diversity including both euryhaline and stenohaline species the ridges are huge elongated sand bodies several kilometres wide 10 60 km long and up to 20 m thick and occur in groups with a spacing of several to 10 km normally they are parallel with each other extending in the direction of the tidal currents the field of tidal sand ridges on the east china sea shelf covers an area of 57 000 km2 tidal sand ridges in the east china sea and the southern yellow sea were formed in estuarine and shallow shelf environments where strong tidal currents reworked transported and redeposited large amounts of relict sands from older deltaic and fluvial sediments the development of tidal sand ridges in estuary mouth areas is accompanied by a net sand transport from the shelf into the estuary the evolution of tidal sand ridges is closely related to transgressions active tidal sand ridges are formed during sea level rises they show distinct morphology and active migrations in a lateral as well as in a landward direction they are generally in equilibrium with present day tidal processes and their distribution patterns are related to the flow field of the tidal currents as the sea level rises further these tidal sand ridges become moribund sand bodies with less distinct morphologies their upper surfaces are covered by a thin calcareous rich layer with very high contents of foraminifera tests reflecting a submarine hiatus condition on the shelf during the highstand period during the subsequent steady fall in sea level tidal sand ridges are often buried by fine grained shelf and prodelta sediments they have therefore a good chance of being preserved in stratigraphic records the sequential buildup during a sea level rise tr tract and a subsequent sea level fall hs and ls tract would consist of estuarine channel and tidal flat facies tidal sand ridge facies shelf mud facies delta facies and fluvial facies in an ascending order tidally dominated estuary conditions may also occur when a major distributary is abandoned such as at the northern branch of the modern changjiang river mouth where the accumulation of sand from an abandoned delta lobe and the development of tidal sand ridges have been observed the observed features have important implications for the subsurface recognition of fossil tidal sand ridges for the reconstruction of the regional palaeogeography and transgressional history and for the prediction of potential reservoir sandstones

ancient shelf ridges a potentially significant component of the transgressive systems tract case study from offshore northwest java detailed stratigraphic evaluation of three dimensional 3 d seis mic volumes calibrated with well log and core data from the mio cene section of the offshore northwest java shelf reveals the exten sive presence of preserved shelf ridge deposits these features are long linear bodies ranging from 0 3 to 2 0 km wide more than 20 km long and up to 17 m high on close inspection these features appear to be asymmetric characteristically sharp edged and thicker on one side and gradually thinning with an irregular edge on the other side possible sand waves smaller in scale are observed super imposed on these ridges and oriented oblique to the long axes of the ridges the observed shelf ridge deposits tend to be sand prone and overlie ravinement surfaces the ridges appear to be oriented parallel with the axes of broad paleoembayments associated with the structural fabric of the basin in addition to shelf ridges shelf ribbons possibly less than 5 m thick and less than 100 m wide are also imaged sand ridges are common on modern shelves but significantly less commonly recognized in the subsurface or in outcrop the features observed here represent examples of preserved ancient shelf ridges these ridges are thought to have formed as a result of erosion and subsequent reworking of sand prone deltaic and or coastal plain deposits by shelf tidal currents which became active immediately after shoreline transgression these deposits appear to have migrated across the ancient sea floor and represent an important component of the transgressive systems tract these transgressive systems tract deposits have significant exploration potential because they are commonly sand prone and tend to be encased in shelf mudstone seal facies depending on the degree to which sand is present in interridge locations these linear sand bodies can comprise potential stratigraphic traps begin page 76

a test of analog based tools for quantitative prediction of large scale fluvial architecture outcrop analogs are routinely used to constrain models of subsurface fluvial sedimentary architecture built through stochastic modeling or interwell sand body correlations correlability models are analog based quantitative templates for guiding the well to well correlation of sand bodies whereas indicator variograms used as input to reservoir models can be parameterized from data collected from analogs using existing empirical relationships this study tests the value and limitations of adopting analog informed correlability models and indicator variogram models and assesses the effect and significance of analog choice in subsurface workflows for characterizing fluvial reservoirs a 3 2 km 2 mi long architectural panel based on a virtual outcrop from the cretaceous blackhawk formation wasatch plateau utah has been used to test the methodologies vertical dummy wells have been constructed across the panel and the intervening fluvial architecture has been predicted using correlability models and sequential indicator simulations the correlability and indicator variogram models employed to predict the outcrop architecture have been compiled using information drawn from an architectural database these models relate to 1 analogs that partially match with the blackhawk formation in terms of depositional setting and 2 empirical relationships relating statistics on depositional element geometries and spatial relations to net to gross ratio based on data from multiple fluvial systems of a variety of forms the forecasting methods are assessed by quantifying the mismatch between predicted architecture and outcrop observations in terms of the correlability of channel complexes and static connectivity of channel deposits results highlight the effectiveness of correlability models as a check for the geologic realism of correlation panels and the value of analog informed indicator variograms as a valid alternative to variogram model parameterization through geostatistical analysis of well data this work has application in the definition of best practice use of analogs in subsurface workflows it provides insight into the typical degree of realism of analog based predictions of reservoir architecture as well as the effect of analog choice and draws attention to associated pitfalls

the offshore quaternary sediment bodies of the english channel and its western approaches after a short review of present day surficial sediments on the sea floor of the english channel and its western approaches this paper summarises recent results on the present quaternary sandy accumulations tidal bank systems based on sea floor imaging very high resolution seismic surveys and a few piston cores the english channel a typical funnel shaped tidal shelf is presently starved of terrigenous sediments most of mobile sediments at the sea floor are autochthonous either skeletal carbonates or siliciclastic sands reworked from old littoral deposits or incised valley fills three zones are considered 1 the central and western central channel which is a bedload parting zone characterised by a pebbly lag making up the sole of the quaternary sediments throughout the shelf area 2 the eastern channel a flood dominated area characterised by medium to fine siliciclastic sands mainly of aeolian periglacial origin 3 the western approaches an ebb dominated area with a polygenic sediment cover characterised by coarse carbonate rich gravelly to muddy sands of marine to glaciomarine origin with a diachronous faunal content these sediments are sourced by reworking of a former littoral barrier or incised valley fills the seismic stratigraphy of quaternary sediment accumulations 10 50 m points to the predominant control of tidal dynamics together with the general interplay between the channel morphology and the sea level story the thickest deposits in the eastern channel and western approaches are built up into bank systems whereas the interpretation of the active eastern channel banks finds a general agreement the moribund banks in the western approaches i e the southern celtic banks remains under debate owing to the lack of long cores in our hypothesis both systems were built up during the last post glacial sea level rise the celtic banks would represent the tidal transgressive systems tract whereas the eastern channel banks correspond to the highstand systems tract the architecture of both bank systems is studied from two examples the bassure de baas bank in the eastern channel and the kaiser bank in the western approaches both examples show transgressive features the bassure de baas exhibits from base to top an estuarine mouth barrier a wave erosion surface a shoreface bank and finally a classic tidal bank by contrast the kaiser bank consists of the offshore reworking of fully marine deposits its base would correspond to the amalgamation of the last glacial sea level fall with a strong tidal ravinement surface from base to top the bank underwent tidal bar accretion very large dune field aggradation perched channels incision storm erosion and deposition

late quaternary stratigraphy and development of tidal sand ridges in the eastern yellow sea abstract the eastern yellow sea is characterized by a number of tidal sand ridges which occur as a series of linear sediment bodies in the shelf shelf sand ridges and as a group of individual sand bodies in the nearshore nearshore sand ridges the shelf sand ridges are present in water depths of 50 90 m and show large elongate shapes with a length up to 200 km in contrast the nearshore sand ridges are much smaller in size up to 34 km length and occur in water depths shallower than about 30 m detailed interpretation of seismic and lithologic data using radiocarbon dating to constrain the ages of the ridges has shown that the regional sea level changes played a major role in the existence and development of different morphologic features of these sand ridges the shelf sand ridges developed mainly during the postglacial transgression ca 14 000 9 500 yr b p possibly during episodes of stillstand or very slow rise of sea level the shape of the shelf sand ridges more or less results from an erosional process dominantly acting during the postglacial transgression the substratum of the shelf sand ridges consists of the regressive or lowstand deltaic mud deposits probably formed prior to the last glacial maximum ca 17 000 yr b p in contrast the nearshore sand ridges have undergone tidal action during the recent highstand of sea level ca 7 000 yr b p and show a typical modern geomorphology of erosional sand ridges the substratum of the nearshore sand ridges consists of remnants of the last interglacial tidal deposits large dunes indicate a strong hydrodynamic influence on the entire ridge surface at present

the imprint of time on canadian soil landscapes abstract the imprint of time on canadian soil landscapes reflects the strong influence of repeated quaternary glaciations with most soils having formed on late pleistocene glacial sediments and to a lesser extent holocene non glacial sediments soil chronosequences in these youthful landscapes seldom span the full holocene and have been documented principally in areas of coastal isostatic uplift and shoreline evolution as well as on recessional moraine sequences in the cordillera these chronosequences have placed quantitative constraints on rates of podzolization in environments ranging from coastal temperate rainforest to subarctic longer sequences involving soils and relict paleosols on pleistocene morainal and glaciofluvial surfaces in the central yukon territory record more complex legacies of pedogenesis and landscape evolution but with much coarser time control and many potentially confounding influences of climatic change and disturbance processes older weathered bedrock and regolith can make significant contributions to soil parent materials in several settings 1 in favoured locations where local conditions protected these materials from glacial erosion in southern canada 2 beyond the maximum limits of glaciation principally in northwestern canada and 3 in the arctic where cold based non erosive ice allowed preservation of these materials closer collaborations between pedologists and other quaternary scientists will be needed to ensure a more complete understanding of these complex pedogenic legacies in canadian landscapes

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

eustatic and hydrodynamic controls on the architecture of a deep shelf sand bank celtic sea the architecture of a tidal sand bank in the south eastern celtic sea was examined using very high resolution seismic surveys the bank comprises four depositional units the lowest unit 1 is characterized by gently dipping 1 8 strata that strike parallel to the length of the bank unit 1 is erosionally overlain by unit 2 which forms the bulk of the bank this unit consists of stacked sets of downcurrent dipping 7 12 master bedding formed by climbing sinuouscrested tidal dunes that are up to 20 m high these deposits are locally incised by an anastomosed channel network unit 3 that may represent a buried swatchway system the upper part of the bank comprises wave related deposits that are mainly preserved on the bank flanks unit 4 the outer bank surface is erosional the bank is believed to have formed during the last postglacial sea level rise the facies evolution from unit 1 to unit 3 indicates an upward increase in tidal energy mainly characterized by the thickening of dune cross bed sets in unit 2 the majority of bank growth is inferred to have occurred in water depths of the order of 60 m this evolution was controlled by relative sea level rise which is likely to have caused an episode of tidal resonance with associated strong tidal currents that were responsible for the incision of the deep cross cutting channels of unit 3 the transition to wavedominated sedimentation in unit 4 is related to the decay of resonance with continued sea level rise

surficial sedimentology of the middelkerke bank southern north sea detailed surficial investigations over the middelkerke bank a tidal sand bank in the southern north sea revealed the relationship between morphology surficial structures and grain size parameters data from 85 grab samples all over the bank show that on a bank normal profile the coarser caco3 rich and badly sorted sediments are generally located near the highest point of the bank seaward at the northern end and landward at the southern end sedimentary structures were studied from 239 boxcores sampled on all the morphological units of the bank crest flanks and adjacent channels in the shallower parts foreset beds are preserved while in the deeper zones intense bioturbation arises and destroys any structure the combination between these data and the virtual absence of wave induced structures indicates that the main agents responsible for the bank shaping are the tidal currents

a meta analysis of reef island response to environmental change on the great barrier reef reef islands on the great barrier reef are influenced by a range of environmental factors a meta analysis of 103 islands is presented to express variation in island size area and volume as a function of latitudinal and cross shelf gradients in regional oceanographic factors exposure to incident waves tidal range and tropical cyclone frequency and local physical factors position on the shelf area length and depth of supporting reef platform vegetative cover models performed well for unvegetated sandcays r2 0 89 vegetated sandcays r2 0 72 and low wooded islands r2 0 78 with a moderate level of variation explained when all islands were simultaneously regressed r2 0 58 future island dynamics were simulated for anticipated changes in cyclone regime wave activity and sea level for 38 islands mapped on the 1973 royal society and universities of queensland expedition to the northern great barrier reef change over the same 22 year period 1973 1995 was determined and the relative magnitude of observed and modelled changes was compared and found to be consistent through rank correlation analysis 0 84 for unvegetated sandcays 0 81 for vegetated sandcays simulations of island area or volume change from 2000 to 2100 indicated that under a 30 decrease in tropical cyclone activity unvegetated sandcays continue to accrete at a lower rate whereas all island types erode under a 38 increase in tropical cyclone activity vegetated sandcays initially accrete at higher levels of cyclone activity entering an erosive state with a 60 increase in activity low wooded islands are unresponsive to environmental changes modelled a sensitivity analysis of vegetated and unvegetated sandcays indicated that the presence of vegetation increases the tropical cyclone activity threshold at which islands begin to erode greatest sedimentary losses occur within the central band of high cyclone activity between cooktown and mackay copyright 2015 john wiley sons ltd

sedimentology of a subtidal tide dominated sand body in the yellow sea southwest korea abstract odanam satoe a subtidal tide dominated sand body in the yellow sea korea is linear in plan and asymmetrical in cross section it consists of fine to medium grained well sorted subangular sand bedforms consist of high amplitude 1 2 m sandwaves on the lower flanks of the gentler sloping bar surface and medium amplitude 0 5 1 m sandwaves on the sand body trough adjoining the steeper face the bar crest and shallower parts of the gently sloping bar surface bedforms are absent on the relatively steeper bar surface which is characterized by 2 slopes bedform orientation on the gentler slope is oblique by 30 to the bar crest parallel to the sand body crest on the crest itself and opposite to the steeper sand body face in the trough below the steeper slope of the bar bottom current velocity data show that tidal currents are semi rotary with a flood time velocity asymmetry over the gentler slope and ebb time velocity asymmetry over the steeper slope during most of the tidal cycle tidal current flow parallels bar elongation over the steeper slope whereas over the gentler slope tidal current flow is directed at 30 to the bar crest and changes to normal to the crest one hour prior to low tide bedform orientation mapped with side scan sonar shows agreement with these flow directions sand dispersal around the sand body is controlled by time velocity asymmetry and partial rotary flow directions of tidal currents this circulation causes not only a trapezoidal mode of grain dispersal but also westerly migration of the sand body documented from comparative bathymetric surveys in 1964 and 1980

celtic sea linear tidal sand ridges the irish sea ice stream and the fleuve manche palaeotidal modelling of a transitional passive margin depositional system abstract the linear tidal sand ridges ltsr of the celtic sea constitute the largest examples of their bedform type on earth previous sedimentological and seismic stratigraphic interpretation suggests that the ltsr are moribund tidally remobilised sediments representing the transgressive systems tract this interpretation is supported by two dimensional finite difference model reconstructions of the m 2 tide forced using the output from a glacial isostatic adjustment model to derive palaeotopography and a global ocean model to derive the tides on the ocean boundary used here to reconstruct peak bed stress vectors for the celtic sea for timesteps covering the transgression since the last glacial maximum last 21 ka these data are coupled with interpretation of recent published observations on the outer shelf depocentres of the fleuve manche and the irish sea ice stream isis to confirm that the ltsr distribution is consistent with modelled sand transport paths during transgression the main phase of ltsr growth was between 20 cal ka and 12 cal ka ridge axis orientations reflect the final phase of ltsr construction around 12 cal ka with some later growth of the most southerly ltsr as late as 10 cal ka ltsr growth was from the sw across the shelf towards the ne strong tidal pumping of sediments into slope canyon heads on the outer shelf occurred between 20 cal ka and 12 cal ka contributing to turbidite activity and the growth of the celtic and armorican deep sea fans it is proposed that 1 the fleuve manche shelfal estuary delta and the irish sea ice stream isis shelf fan were the main sediment depocentres supplying the growing ltsr 2 the lack of sediments available in the western channel limited ltsr growth in this area and that the easterly termination of the ltsr in this sector results from sediment starvation and 3 the northeasterly termination in the celtic sea sector is a function of declining peak bed stresses rather than sediment starvation the celtic sea margin represents a passive margin depositional system transitional between true glacial ice stream trough mouth fan systems to the north and the fluvial canyon systems characteristic of the margin to the south this interpretation therefore complements studies of macroscale sedimentation linked to glaciation on the continental margins of the north atlantic

quaternary seismic stratigraphy and paleoenvironments on the continental shelf of the east china sea abstract paleoenvironments and stratigraphy have been interpreted from 4380 km of seismic profiling collected during a geological and geophysical cruise on the continental shelf of the east china sea ecs undertaken in 1996 the geophysical data are correlated with a borehole situated on the outer shelf obtained by shanghai marine geology bureau indicating that six seismic units have been preserved since oxygen isotope stage 6 including four regressive transgressive cycles seismic units u2 u3 u4 u5 u6 and u7 are interpreted to correspond respectively to oxygen isotope stages 1 3 5 and 6 implying that sediment partitioning and sequence architecture in the ecs have been controlled by glacio eustasy and global climate changes alternating continental and marine strata corresponding to glaciation and interglaciation are well preserved on the outer shelf of the ecs most of the cold environment strata which formed on the outer shelf during oxygen isotope stages 2 and 4 are too thin to be recognized on sig 600j because of resolution but corresponding erosion surfaces exist seismic unit u7 is widespread over the shelf extending to the continental edge and showing little variation in thickness as the regression was pronounced and lasted a long time thus u7 can be used as a marker layer for correlation of quaternary strata on the shelf of the ecs post glacial transgression is obvious in the ecs marine strata with varied thickness were developed in the shallow sea of the inner shelf thinning toward the outer shelf the continental shelf of the ecs has been influenced by pacific tide wave systems for a long time forming tidal sand ridge sequences developed during transgressions corresponding to oxygen isotope stages 7 or 9 5 3 and 1

hydrodynamics and sedimentation in wave dominated coastal environmentsshoreface morphodynamics on wave dominated coasts an open ocean shoreface typical of long wave dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents sand on the middle and lower shoreface as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents storm events have been studied and modeled for the shoreface off tiana beach long island the dominant effect of coastal frontal storms is to cause significant shore parallel bedload transport with important shore normal secondary components these storms tend to result in net offshore transport of sand removed from the beach and surf zone systems the bedload transport during a storm is convergent on the shoreface leading to accretion most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf longer term equilibrium can be maintained by slow return of sand up the shoreface during non storm conditions annual and geologic time scale budgets of shoreface sand transport and sedimentation yield equilibrium net accretion or net deposition the annual balance results from an integration of the event scale bedload transport patterns and morphologic responses these processes and responses have feedback mechanisms which stabilize the system over longer but not geologic time scales geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event scale shoreface and transporting processes providing the mechanism to produce the changes in long term morphology and sedimentation patterns in the area of study the long term pattern is one of net shoreface erosion and the permanent loss of sand to the shelf floor

pleistocene forced regressions and tidal sand ridges in the east china sea abstract tidal sand ridges are common features on modern shelves but only few examples of such preserved sand bodies are described in pleistocene deposits in the stratigraphic record some sand bodies encased in shales previously interpreted as sand ridges have been reinterpreted as shoreface deposits more than 5000 km of high resolution seismic data from the east china sea correlated to geotechnical boreholes and shallow cores demonstrate the potential of sand ridge preservation and allow reconstruction of the depositional history of pleistocene fourth order 100 kyr depositional sequences a high subsidence rate of about 300 m myr allows the preservation of three elementary sedimentary facies constitutive of a motif which was repeated during glacio eustatic cycles they consist of 1 regressive marine prodeltaic prograding wedges 2 estuarine and continental deltaic facies and 3 transgressive sand ridges similar in shape and orientation to modern sand ridges major discontinuities traceable over the entire outer continental shelf along distances of hundreds of kilometers are transgressive and regressive surfaces of marine erosion whereas sequence boundaries formed by fluvial erosion are difficult to identify on this low gradient shelf because of the asymmetry of the pleistocene glacio eustatic cycles most of the preserved sedimentary record with the exception of sand ridges corresponds to forced regressive deposits deposits that formed during a seaward shift of the shoreline due to relative sea level lowering

the shallow marine architecture knowledge store a database for the characterization of shallow marine and paralic depositional systems abstract the shallow marine architecture knowledge store smaks is a relational database devised for the storage of hard and soft data on the sedimentary architecture of ancient shallow marine and paralic siliciclastic successions and on the geomorphological organization of corresponding modern environments the database allows incorporation of data from the published literature which are uploaded to a common standard to ensure consistency in data definition the database incorporates data on geological entities of varied nature and scale i e surfaces depositional tracts architectural elements sequence stratigraphic units facies units geomorphic elements including attributes that characterize their type geometry spatial relations hierarchical relations and temporal significance furthermore geological entities are assigned to depositional systems or to parts thereof that can be classified on multiple parameters e g shelf width delta catchment area tied to metadata e g data types data sources the smaks permits the quantitative characterization of modern and ancient shallow marine and paralic clastic depositional systems it aims to serve as a repository of analogue information for hydrocarbon bearing successions and as a research tool that can be applied to aid the development of facies models or to assess the sensitivity of depositional systems to particular controlling factors for example to demonstrate the wide applicability of the database in fields of both fundamental and applied research example database output is presented that i includes data from wave tide and fluvial dominated shallow seas and sedimentary successions and ii covers a wide depositional spectrum from backshore to shelf edge settings the examples include information on the facies organization of different types of paralic sub environments on the hierarchical arrangement of architectural elements that form deltaic constructional units in quaternary deltas on the morphometry of modern and quaternary tidal sand ridges and on the geometry of parasequence scale nearshore sandstone belts from the upper cretaceous of the western interior seaway in utah usa

shoreface morphodynamics on wave dominated coasts abstract an open ocean shoreface typical of long wave dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents sand on the middle and lower shoreface as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents storm events have been studied and modeled for the shoreface off tiana beach long island the dominant effect of coastal frontal storms is to cause significant shore parallel bedload transport with important shore normal secondary components these storms tend to result in net offshore transport of sand removed from the beach and surf zone systems the bedload transport during a storm is convergent on the shoreface leading to accretion most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf longer term equilibrium can be maintained by slow return of sand up the shoreface during non storm conditions annual and geologic time scale budgets of shoreface sand transport and sedimentation yield equilibrium net accretion or net deposition the annual balance results from an integration of the event scale bedload transport patterns and morphologic responses these processes and responses have feedback mechanisms which stabilize the system over longer but not geologic time scales geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event scale shoreface and transporting processes providing the mechanism to produce the changes in long term morphology and sedimentation patterns in the area of study the long term pattern is one of net shoreface erosion and the permanent loss of sand to the shelf floor

transgressive sand ridges on the mid shelf of the southern sea of korea korea strait formation and development in high energy environments abstract the mid shelf of the southern sea of korea korea strait is covered by a series of shore parallel sand ridges up to 63 km long 3 9 km wide and 22 m thick the ridges are a moribund type but show well organized dipping strata indicating appreciable progradation the submerged paleo channel system the paleo seomjin river associated with the sand ridge field suggests that the ridges primarily originated from river mouth sandy shoals which subsequently developed into shore parallel linear sand bodies in high energy environments the combined effect of coastal tidal and longshore and offshore ocean currents was possibly responsible for shore parallel sediment transport and growth of the ridges 14c dates core lithology and sea level data suggest that the sand ridges mainly formed and developed during the middle period of the postglacial transgression they are postulated to have developed sequentially from offshore to onshore in response to sea level rise during that time very slow sea level rise and high sediment supply through the paleo channel system probably provided favorable conditions for forming the sand ridges the ridges became inactive during the late transgression period as a result of a substantial reduction of wave and current strength and remained on the mid shelf

stratigraphic uncertainty in sparse versus rich data sets in a fluvial deltaic outcrop analog ferron notom delta in the henry mountains region southern utah the turonian notom delta is one of the ferron fluvial deltaic wedges deposited in the cretaceous foreland basin of north america and is well exposed in the henry mountains region utah this article uses variable sampling of measured sections of the fluvial deltaic wedge along a 19 mi 30 km outcrop belt to address correlation uncertainties in sparse data sets such as are common in subsurface studies a high resolution sequence stratigraphic analysis based on 58 measured sections extensive walking out of beds and field photomosaics shows that the wedge is composed of 43 parasequences 18 parasequence sets and six depositional sequences resampling the outcrop belt with 13 sections provides a sparse data set correlations using the data set show considerable uncertainties fluvial complexity is greatly underestimated and in the extreme case only 40 of the fluvial bodies are identified overcorrelation results in as much as 400 exaggeration of sandstone width and thickness some of the uncertainties can be reduced by incorporating nonmarine sequence stratigraphic models and various techniques that allow a more reasonable evaluation of fluvial body geometry with sparse data uncertainties also arise in marine successions a key challenge is to identify and correlate the small scale units particularly forced regressive deposits many of their diagnostic features that can be easily recognized from outcrops and cores may not be as easily detected from well logs and on seismic data in subsurface studies where sparse data are observed integrating detailed facies analysis cores and sequence stratigraphic concepts is critical to predict the occurrence and understand the architecture of such deposits

late quaternary transgressive and highstand systems tracts in the northern east china sea mid shelf abstract analysis of very high resolution 3 5 khz seismic profiles and sediment data from the northern east china sea mid shelf region reveals that the sedimentary sequence above the acoustic basement consists of five late quaternary sedimentary units comprising transgressive and highstand systems tracts formed after the last glacial maximum the transgressive systems tract includes four units 1 incised valley fill unit i 2 transgressive estuarine deltaic complex unit ii 3 transgressive sand sheet unit iii and 4 tidal sand ridge unit iv the lower two units units i and ii representing a paralic environment consist of sediment preserved from shoreface erosion the upper units units iii and iv corresponding to a marine environment consist of sediments produced through shoreface erosion during the holocene transgression a ravinement surface separates the lower and the upper units the highstand systems tract is composed of a distal mud patch unit v derived from the huanghe and changjiang rivers in china dispersal and deposition of this modern mud are largely controlled by the regional circulation pattern and sediment supply

the fluvial record of climate change fluvial landforms and sediments can be used to reconstruct past hydrological conditions over different time scales once allowance has been made for tectonic base level and human complications field stratigraphic evidence is explored here at three time scales the later pleistocene the holocene and the historical and instrumental period new data from a range of field studies demonstrate that croll milankovitch forcing dansgaard oeschger and heinrich events enhanced monsoon circulation millennial to centennial scale climate variability within the holocene probably associated with solar forcing and deep ocean circulation and flood event variability in recent centuries can all be discerned in the fluvial record although very significant advances have been made in river system and climate change research in recent years the potential of fluvial palaeohydrology has yet to be fully realized to the detriment of climatology public health resource management and river engineering

models for guiding and ranking well to well correlations of channel bodies in fluvial reservoirs a probabilistic method has been devised to assess the geologic realism of subsurface well to well correlations that entail the lateral tracing of geologic bodies across well arrays with constant spacing models of geo body correlability based on the ratio between correlatable and penetrated geo bodies are obtained from total probabilities of penetration and correlation which are themselves dependent on the distribution of lateral extent of the geo body type employing outcrop analog data to constrain the width distribution of the geo bodies it is possible to generate a model that describes realistic well to well correlation patterns for given types of depositional systems this type of correlability model can be applied for checking the quality of correlation based subsurface interpretations by assessing their geologic realism as compared with one or more suitable outcrop analogs the approach is illustrated by generating total probability curves that refer to fluvial channel complexes and that are categorized on the basis of outcrop analog classifications e g braided system system with 20 net to gross employing information from a large fluvial geo body database fluvial architecture knowledge transfer system fakts which stores information relating to fluvial architecture from these total probability functions values can be drawn to adapt the correlability models to any well array spacing the method has been specifically applied to rank three published alternative interpretations of a stratigraphic interval of the travis peak formation texas previously interpreted as a braided fluvial depositional system in terms of realism of correlation patterns as compared to 1 all analogs recorded in fakts and considered suitable for large scale architectural characterization and 2 a subset of them including only systems interpreted as braided

architectural stacking patterns of the ebro delta controlled by holocene high frequency eustatic fluctuations delta lobe switching and subsidence processes abstract during the late pleistocene and holocene 125 ka b p to present a type 1 4th order depositional sequence comprising regressive lowstand transgressive and highstand system tracts formed worldwide the holocene 10 ka b p to present part of this contains the latest and present highstand systems tract hst within this and the underlying transgressive systems tract tst of the ebro delta in northeastern spain higher frequency 5th to 6th order sea level fluctuations are recognised these form retrogradational and progradational high frequency depositional sequence sets within the tst and hst respectively each high frequency sequence comprises 1 a basal highly reflective shell lag associated with an erosional transgressive surface 2 aggradational deposits which seawards consist of a wedge of marine clays with transparent seismic facies but inland are represented by thick peats 3 progradational deposits composed of sandy delta front facies displaying slope clinoforms these pass seawards into prodeltaic grey silts and landwards into red silts and pebbly sands of delta plain facies the progradational deposits downlap towards their bases the aggradational deposits formed in response to a period of rising sea level and a rapid increase in accommodation space progradation began when sediment supply to the delta exceeded accommodation space as a result of relative sea level fall the relative sea level curve for the delta has a stepped character caused by the punctuation of the 4th order sea level trend by higher frequency eustatic fluctuations as well as by high subsidence rates of about 1 75 mm per year the tst comprises retrogradational parasequences that onlap the underlying pleistocene gravels the maximum flooding surface separating the tst from the hst was formed about 6900 yrs b p on the basis of14c dating of peats the hst comprises progradational deltaic and aggradational units stacked as progradational high frequency parasequence sets the hst of the ebro delta is compared with other deltaic sequences around the world in particular with that of the mississippi delta a tentative chronology of the high frequency climatic and eustatic oscillations influencing deltaic sedimentation globally over the last 7000 years is presented

tidal current ridges in the southwestern yellow sea abstract large tidal current ridges tidal sand banks in the southwestern yellow sea are located offshore of northern jiangsu province china these ridges radiate to a depth of 20 30 m the dimensions of the ridge system are about 200 km long and 90 km wide their morphology indicates the strong influence of tidal currents the ridges are composed of well sorted fine sands size range is 2 4 the grain size distributions of the sands show that the sands are transported and deposited by tidal currents the ridge system formed on the abandoned yellow river and ancient yangtze river deltas has an abundant sand supply from the former deltas of particular importance is the existence of two tidal wave systems in the yellow sea the rotary ti al wave system in the southern yellow sea and the pacific progressive tidal wave system propagated into the southern ridge area of the southwestern yellow sea under the interaction of the two tidal wave systems the huge tidal current system in the southwestern yellow sea has formed

overbank and channelfill deposits of the modern yellow river delta abstract the huanghe is noted for its high transport rate of silt and clay which may reach depth averaged values of 200 kg m 3 during peak discharge the sediment load transported through the river on entering the delta plain amounts to 1012 kg per year in contrast to most other large deltas only one distributary channel is active at any one time the high sediment load causes the rivermouth to prograde at a yearly rate of 1 4 km into the shallow less than 20 m deep bohai gulf the vertical aggradation of the channel belt and mouth bar complex is also rapid decimetres per year on average so that after a normal average of twelve years increasing channel instability and avulsion create the start of a new delta lobe a series of satellite images covering the last fifteen years has provided insight in the evolution of the river pattern as well as the progradation of the delta front a newly developed distributary passes from a multichannel to a single straight channel system and ends with the formation of meanders the protruding mature delta lobe shows a radiating pattern of crevasse channels overbank crevasse deposits are made of vertically stacked dm scale waning flow sequences structurally characterized by from bottom to top small scour and fills even parallel lamination and climbing ripple crosslamination accumulation rates on crevasse splays can be predicted on the basis of estimated river sediment discharge it can be concluded that each sequence has been deposited within a few hours and that tidal waterlevel fluctuations may have played a role in the generation of a single sequence

parameterizing parasequences importance of shelf gradient shoreline trajectory sediment supply and autoretreat the basic reservoir flow unit in shallow marine depositional systems is the parasequence since it is bounded top and base by regionally extensive shales that can form barriers to fluid flow as a result it is the key stratigraphic unit requiring parameterization for both exploration and development purposes a database comprising 3385 measurement points from 385 parasequences from 28 locations and 16 different passive margin and foreland basins was compiled from outcrop and subsurface data analysis of the data suggests that a mean value for parasequence thickness is 17 m 56 ft mean parasequence sandstone fraction is 0 60 and mean shoreface sand body thickness is 8 m 26 ft the mean maximum parasequence progradation distance is 23 km 14 mi the results indicate that there are two critical controls that can significantly vary the parameter values stated above 1 stacked shoreline trajectory or systems tract and 2 shelf gradient the analyses indicate that shelf gradient is the most important parameter that has a first order control on parasequence properties shelf gradient in the ancient can be approximated to high gradient or low to moderate gradient categories via analysis of parasequence thickness change versus progradation distance from wells mean parasequence thickness or mean progradation distance from seismic attribute data parasequence progradation distance is to some degree predictable if stacked shoreline trajectory shelf gradient category and mean parasequence thickness are known the data suggest that there are two types of parasequences accommodation dominated and supply dominated parasequences the progradation distance of these parasequences are controlled by delta autoretreat mechanisms modulated by the combination of fifth and fourth order milankovitch scale orbitally forced climate change driven sediment supply cycles interacting with eustatically and tectonically driven accommodation cycles

pre requisites processes and prediction of chlorite grain coatings in petroleum reservoirs a review of subsurface examples abstract deeply buried reservoirs containing chlorite coated quartz sand grains commonly have higher than expected porosity and permeability although prediction of such positive anomalies still remains elusive a total of 54 published examples based on information and data from 62 scientific papers was collated quantification of some of the most common parameters including depositional environment age and latitude of sand deposition effect on reservoir quality and chemical composition of chlorite is presented the dataset indicates that chlorite coats are found in sandstones deposited in a range of depositional environments but most commonly occur in delta related environments 44 with fluvial environments the second most common 19 age relationships indicate that there is an overall exploration bias in published examples with chlorite coats becoming increasingly common through time the latitude at the time of deposition of sands with chlorite coats is wide 60 n 60 s and indicates that temperate and tropical climates are important for the generation of this clay mineral chlorite can have a variable effect on reservoir quality but is typically positive iron rich chlorites occur overwhelmingly in coastal environments while mixed iron and magnesium rich chlorites are principally found in marine and terrestrial sandstones analysis of these factors suggests that hinterland geology basinal soil development and geochemical weathering and proximity to river systems are essential to the formation of chlorite precursor phases these characteristics have been combined to define situations where chlorite coats were more likely or more unlikely to form these parameters will provide insights into the formation of chlorite and to further refine predictive models for the presence or absence of chlorite coated sandstones

sedimentology and stratigraphy of a tidal sand bank in the southern north sea abstract a set of 125 vibrocores collected on the basis of a dense grid of high and very high resolution seismic coverage over a tidal sand bank the middelkerke bank provides a unique opportunity to reconstruct the stratigraphy and sedimentary facies succession of such a large tidal sand body five sedimentary facies are distinguished they range from clay to pebble and display various types of bedding and lithologies corresponding to different depositional environments a succession of four late quaternary units are defined on the basis of the stratigraphic framework given by the seismic grid the first unit represents the infill of a palaeovalley system by tidally influenced sedimentary facies it is followed by extensive and thick lagoonal or sub tidal deposits the third unit reveals the development of a landward prograding storm dominated sand bar this unit is dominated by clean fine sand the last unit corresponds to the present day tidal sand bank it shows the typical offshore tidal sand bank facies cross bedded sand prograding in an offshore direction like other banks located in a more offshore position the middelkerke bank is a composite bank incorporating facies which do not occur in classic tidal sand banks

the celtic sea banks an example of sand body analysis from very high resolution seismic data very high resolution seismic data from the kaiser i hind sand bank southern celtic sea recently highlighted the internal structure of the enigmatic celtic banks which are among the deepest and largest shelf sand ridges the main body of the bank is made up of 4 seismic depositional units which reflect a transgressive evolution new data on the detailed architecture of two of these units allow discussion of bank growth in terms of either 1 a channel levee system preserved both by lateral migration and aggradation of the channels or 2 a package of large offshore tidal sediment bodies bar chains and or giant dunes careful geometrical observations of seismic discontinuities make the second hypothesis more likely the unit architecture is analysed in terms of long to short term processes of build up long term processes are evinced by the landward stacking of erosive sub units in response of the last post glacial sea level rise whereas short term processes control the seaward progradation of sand bodies and fills due to the ebb predominance of the western channel approaches

on the geological significance of clastic parasequences abstract parasequences recognized in clastic sedimentary successions of shallow marine origin are considered by some geologists to be the fundamental building blocks of depositional sequences even though problems in their definition and application have been identified by others who instead advocate their abandonment as formal sequence stratigraphic units to elucidate the geological significance of clastic parasequences and inform the debate on their use in stratigraphy a quantitative characterization of the geometry facies characteristics and timescale of deposition of 1163 parasequences has been undertaken based on a synthesis of data from outcrop and subsurface studies that are available in the scientific literature through a database compilation the attributes of the studied parasequences are analysed with respect to the interpreted geological origin of the units and with consideration of sources of bias and uncertainty particular emphasis is placed on assessing the following i the importance of heuristics and of data types and coverage in the recognition of parasequences ii differences in parasequence characteristics observed across deltaic and shoreface depositional systems and between the quaternary and the ancient rock record iii possible explanations for the range in timescales of deposition of parasequences and iv the role of autogenic dynamics on the development of deltaic parasequences partly based on a comparison with the recent evolution of modern deltas the results demonstrate that parasequence definition and physical correlation suffer from subjectivity and that significant variability exists in the spatio temporal and architectural attributes of clastic parasequences this gives rise to uncertainty that affects the use of parasequences as a framework for comparison of the architecture of packages of strata originating via shoreline regression this uncertainty must be considered when using analogue data for subsurface predictions or when attempting comparative studies of clastic successions

quaternary coastal plains as reservoir analogs wave dominated sand body heterogeneity from outcrop and ground penetrating radar central santos basin southeast brazil abstract sub seismic sand body characterization depends largely on understanding the heterogeneities observed in outcrops of equivalent depositional settings to subsurface reservoirs reservoir analogs outcrop information however rarely covers the whole depositional system ground penetrating radar gpr on the other hand is a powerful tool for the high resolution visualization of sand rich deposits in the shallow subsurface allowing for the description of their internal architecture relationships with depositional systems and its larger scale stratigraphic evolution the internal character of radar patterns can be interpreted with respect to facies seen in exposures leading to the prediction of heterogeneities below radar resolution in this paper we use gpr and outcrops to describe the heterogeneity of quaternary coastal plain deposits from central santos basin parana state southern brazil where pleistocene and holocene wave dominated regressive barriers and transgressive lagoons and estuaries were formed under the influence of quaternary sea level and climatic changes sedimentary facies reveal the predominance of sand deposited under the influence of tidal processes fair weather and storm wave processes radarfacies indicate a tendency of progradation of beach face reflectors over subtidal radarfacies within two regressive successions separated by a regional unconformity interpretation of gpr resulted in the definition of 13 radarfacies arranged in three associations reflecting major depositional systems 1 strandplains formed by prograding beach dune ridge sets over subtidal deposits 2 spit inlets with progradation of beach faces over subtidal deposits and longshore accretion of spits and 3 paleolagoons paleoestuaries sedimentary facies indicate that strandplains and spit inlets are predominantly sandy while a muddy composition is expected in paleolagoons paleoestuaries the distribution and evolution of these systems were controlled by base level oscillations and or sediment supply that resulted in the formation of two regressive barriers separated by a wave ravinement surface configuring two parasequences with a wide variety of inter and intra sand body heterogeneities this arrangement imprints a relatively high degree of compartmentalization within deposits that are traditionally considered continuous and homogeneous therefore the quaternary coastal plain of parana can be used as an analog for compartmentalized coastal reservoirs

depositional patterns of sand ridges in tide dominated shallow water environments yellow sea coast and south sea of korea abstract the continental shelf of the yellow sea and the korean south sea is a tide dominated shelf a number of sand ridges occur in this area which form bathymetric highs surveyed were one large sand ridge jangan satoe along the western yellow sea coast and a group of mid shelf sand ridges in the south sea to delineate their depositional pattern and probable origin in tide dominated shallow water environments analyses of sediment samples side scan sonographs and seismic profiles reveal that these ridges show regionally different characteristics in morphology bedforms and sediment the sand ridge in the yellow sea shows a composite form of various bedforms including sand waves and megaripples this ridge is interpreted to be in an accretional active stage maintained by strong tidal currents in contrast the sand ridges on the mid shelf of the south sea show rounded single forms without bedforms on them they are interpreted to represent moribund type sand ridges in the shelf environment which were formed near the shoreline during the holocene sea level transgression these ridges developed off the paleo seomjin river during a period of a stillstand or slow sea level rise approximately between 10 000 and 7000 yrs b p

the neogene succession of the south western approaches great britain the outer continental shelf in the south western approaches is underlain by an oceanward dipping wedge of neogene strata up to 400 m thick that is divisible into three units a the early to mid miocene parallel bedded calcilutites of the jones formation which rest with a marked eastward overstep on palaeogene and cretaceous strata b the mid to late miocene cockburn formation which consists of calcarenites fashioned into a series of linear tidal ridges that are separated locally by an unconformity from the underlying unit c the plio pleistocene little sole formation which sits with a planar unconformity on the miocene strata and is divisible into a lower wedge like member restricted to near the shelf edge and an upper more widespread sheet like member palaeo bathymetric and seismo stratigraphic evidence indicates that the shelf and adjacent land areas have suffered epeirogenic movement since the early miocene

bedforms of the canadian eastern seaboard a comparison with global occurrences this paper presents a compilation of sedimentary bedforms identified from acoustic and seismic records collected over the southeastern canadian continental shelf in order to make the compilation it was found necessary to firstly review and synthesise the various terminologies used to describe the bedforms found and thereafter to relate the subsequent terminology to any diagnostic generic characteristic identifiable from the records sand waves are considered to be those forms that are composite in nature and are generated solely by the action of superimposed megaripples these latter features are identifiable adopting the classification of dalrymple et al 1978 which proves adequate for the acoustic differentiation of 2 d and 3 d types though we observed a greater coherence in bedform spacing of the 2 d types than reported hitherto sand ridges were adequately defined and recognised using the description of swift et al 1978 with respect to storm generated ridges and that of off 1963 and others with respect to tidal current ridges such ridges appear not to be uniquely described by ratios of their metrics the bedforms on the southeastern canadian continental shelf are abundant and wide spread virtually all types of bedforms recognisable on the u s shelf are present to the north the majority of these bedforms appear to be storm generated and are considered intermittently active many of the sand waves s s have no measureable relief though retaining their distinctive spatial geometry both active and moribund sand ridges were found of these ridges both tidal and storm generated types were identified the storm generated ridges were further broken down into shoreface connected ridges and offshore ridges a metrical analysis of the various bedforms show that a differentiation into stable bed phases can be made using height length ratios provided the bedforms are active and fully developed there is some overlap between megaripples and small sand waves and indeed between 2 d and 3 d megaripples yet the distinction is good between sand waves and sand ridges even moribund types sand ribbons in general can be confused with moribund sand waves and megaripples a detailed morphological examination is required to distinguish each feature data from sand ridges of the eastern canadian shelf combined with data from similar features found globally shows that ridge heights tend to cluster into three distinctive modes these modes are at heights of 7 13 and 27 m the first mode is correlated with storm generated ridges the second with tidal current ridges and the third possibly with submerged barrier islands

molybdenum isotope evidence for global ocean anoxia coupled with perturbations to the carbon cycle during the early jurassic relatively brief periods of severe paleoenvironmental change during the jurassic and cretaceous were associated with the widespread accumulation of organic rich marine deposits termed oceanic anoxic events oaes these intervals involved abrupt global warming of 5 10 c higher rates of continental weathering elevated extinction rates and large scale perturbations to the global carbon cycle the major oaes also overlapped temporally the emplacement of large igneous provinces however despite being known as oaes the extent of seawater anoxia at those times is undefined and the causative processes remain unclear here we show how changes in seawater molybdenum isotope ratios a proxy for seawater anoxia during the toarcian early jurassic oae define the onset and expansion of oxygen deficient conditions our data also place constraints on the areal extent of marine anoxia during the event and demonstrate that anoxia expanded and contracted periodically broadly in line with precession driven changes in 13 corg despite their intermittent occurrence over geological history oaes have an important contemporary relevance because the magnitude and high rates of environmental change then were broadly similar to those occurring at the present day

the use of spectral recomposition in tailored forward seismic modeling of outcrop analogs spectral recomposition is an improved methodology for generating forward seismic models of outcrop analogs that make use of the full range of frequencies found within real world seismic volumes it overcomes the issue common to conventional forward seismic models in which single peak frequencies are modeled with the resultant models not capturing the range of frequency content that is found in the real world image this variable frequency content of real world seismic volumes has long been known to contain more detailed information within different spectral bands which forms the basis of the spectral decomposition process in which different spectral frequencies can correlate to different stratigraphic thicknesses for example in this article we introduce and illustrate the use of a new method termed spectral recomposition spectral recomposition is a poststack seismic method operating in the frequency domain that recomposes forward seismic models generated at separate peak frequencies to derive a final image which has a frequency spectrum similar to that of a targeted real world image using this method forward seismic models can be tailored to specific real world images and be used as a more appropriate comparison between the known outcrop geometries and those that are imaged in the subsurface

sedimentation in the yellow river delta part ii suspended sediment dispersal and deposition on the subaqueous delta abstract rapid deposition and suspended sediment dispersal off the modern yellow river mouth has been examined from the data of topographic maps 1 25 000 suspension and bed sediments current and salinity which were measured in the field the results show that the sedimentation rate of the mouth bar is the highest of all the environments of deposition in the modern yellow river delta about 30 40 of the sediment that the river transports into the sea has been deposited within the mouth bar area rapid deposition of the mouth bar results mainly from kinetic energy dissipation of the river under the influence of three ambient mechanisms these three mechanisms occur simultaneously as shear front movement which obstructs the river s jet like flow small scale circulations where large velocity gradients occur and the bulldozer effect of the tide sensitive zone in the estuary at ebb based on the analysis of morphologic changes the mouth bar can be divided into two morphologic types one is the double lobe and single channel type and the other double channel and single lobe type weak hyperpycnal plumes with small density differences between the river flow and ambient water dissipate rapidly and deposit about 20 of the river sediments on the delta front slope while hyperpycnal underflows from the river mouth can go through the steep delta front slope to form a rise apron along the upper part of the prodelta grain size analysis of suspended sediment shows that the flow can be divided into three layers a tide layer in the upper part and a hyperpycnal layer in the lower part these two layers are normally graded and a transition layer with inverse grading in the mid part the fine suspended sediments have been transported in the hypopycnal plume layer into the prodelta and deep sea such as the north huanghai sea north yellow sea this study indicates that the tidal current field has dominated the distribution of deposition of sediment on the subaqueous delta and the movements of the river effluent and hyperpycnal underflows

historical changes in the yellow river delta china abstract the lower yellow river delta has experienced numerous avulsions during the last 2000 years and the floodplain can be divided into four provinces alluvial fan western plain middle plain and eastern plain coastal deltas the yellow river delta complex is composed of several delta superlobes resulting from shifts in the lower river channel and each delta superlobe consists of several smaller lobes formed by shifts in the distributary channels these two kinds of channel shifts have resulted in a complicated imbrication pattern in the delta complex two imbricated delta superlobes are divided by a reworked bed and buried shelf deposits shelly ridges form the surface boundaries between the various delta superlobes the delta superlobes passed through an active stage a reworking stage and were then finally overlain by later superlobes

architecture and long term evolution of a tidal sandbank the middelkerke bank southern north sea abstract the internal structure of the middelkerke bank one of the flemish banks located in the southern north sea off the coast of oostende belgium has been studied in the framework of the marine science and technology mast program co funded by the european community a dense grid of high and very high resolution seismic profiles has been used as well as several vibrocorings seven major seismic units can be identified in the quaternary sediments bounded by major discontinuities correlated across the whole study area the lower units clearly appear as being deposited during periods of relative low sea level channel infillings shoreface estuarine and or ebb tidal delta deposits the present shape of the bank results partly from recent erosional processes reworking the underlying deposits thus the lower part of the bank as a morphological feature does not consist of offshore tidal sands the master bedding of the upper part of the bank consists of inclined reflectors dipping at an angle of about 5 in the same direction as the bank s steep face these reflectors very similar to those described by houbolt 1968 are interpreted as being the result of alternating periods of deposition and erosion related to the episodic combination of tidal currents and storms

standardizing texture and facies codes for a process based classification of clastic sediment and rock abstract proposed here is a universally applicable texturally based classification of clastic sediment that is independent from composition cementation and geologic environment is closely allied to process sedimentology and applies to all compartments in the source to sink system the classification is contingent on defining the term clastic so that it is independent from composition or origin and includes any particles or grains that are subject to erosion transportation and deposition modifications to folk s 1980 texturally based classification that include applying new assumptions and defining a broader array of textural fields are proposed to accommodate this the revised ternary diagrams include additional textural fields that better define poorly sorted and coarse grained deposits so that all end members gravel sand and mud size fractions are included in textural codes revised textural fields or classes are based on a strict adherence to volumetric estimates of percentages of gravel sand and mud size grain populations which by definition must sum to 100 the new classification ensures that descriptors are applied consistently to all end members in the ternary diagram gravel sand and mud according to several rules and that none of the end members are ignored these modifications provide bases for standardizing vertical displays of texture in graphic logs lithofacies codes and their derivatives hydrofacies hydrofacies codes are nondirectional permeability indicators that predict aquifer or reservoir potential folk s 1980 ternary diagram for fine grained clastic sediments sand silt and clay size fractions is also revised to preserve consistency with the revised diagram for gravel sand and mud standardizing texture ensures that the principles of process sedimentology are consistently applied to compositionally variable rock sequences such as mixed carbonate siliciclastic ramp settings and the extreme ends of depositional systems

a database approach for constraining stochastic simulations of the sedimentary heterogeneity of fluvial reservoirs quantitative databases storing analog data describing the geometry of sedimentologic features are commonly used to derive input for geostatistical simulations of reservoir sedimentary architecture however geometrical information alone is inadequate for the detailed characterization of sedimentary heterogeneity a relational database storing fluvial architecture data has been developed and populated with literature and field derived data from modern rivers and ancient successions the database scheme characterizes fluvial architecture at three different scales of observation recording style of internal organization geometries and spatial relationships of genetic units classifying data sets according to controlling factors e g climate type and context descriptive characteristics e g river pattern the database can therefore be filtered on both architectural features and boundary conditions to yield outputs tailored on the system being modeled to generate input to object and pixel based stochastic simulations of reservoir architecture when modeling heterogeneity with stochastic simulations the choice of input parameters quantifying spatial variation is problematic because of the paucity of primary data and the partial characterization of supposed analogs this database driven approach permits the definition of various constraints referring to either genetic units e g architectural elements or material units i e contiguous volumes of sediment characterized by the same value of a given categorical or discretized variable e g same lithofacies type clay and silt content and others which permit the realistic description of fluvial architecture heterogeneity applications of this database approach include the computation of relative dimensional parameters and the generation of auto and cross variograms and transition probability matrices which are necessary to effectively model spatial complexity

stratigraphy of a north sea tidal sand ridge large sand ridges in the east bank area of the north sea lie in deeper water and are subjected to less powerful tidal currents than the better known norfolk banks further to the south they also lack large scale bedforms on their surfaces the east bank ridges are considered to have formed during the early holocene around 9000 ybp and are now moribund drilling of a 35 m thick ridge from this area has shown a remarkably homogenous stratigraphy the ridge is characterized by 2 stacked slightly coarsening upward sequences of fine well sorted terrigenous sand bioturbation characterizes the top of the sequence with fine laminations and small scale ripple cross strata scattered throughout heavy minerals are diverse and increase in abundance upward

the modern po delta system lobe switching and asymmetric prodelta growth the modern po delta system comprising five main delta lobes has been investigated by integrating vhr seismic surveys recorded offshore from water depths as shallow as 5 m to the toe of the prodelta in about 30 m with accurate historical cartography extending back several centuries previous studies give sedimentological and geochronological information from precisely positioned sediment cores this combined historical and stratigraphic reconstruction of the modern po prodelta allows volumetric reconstructions indicating an average sediment load of 9 4 10 6 ty r 1 for po di pila and po di goro gnocca lobes this estimate is remarkably consistent with the total sediment load of 11 5 10 6 ty r 1 available for parts of the last century from a gauge station at the apex of the delta plain in pontelagoscuro these integrated stratigraphic studies allow to explain the key characters of the po delta system a the marked asymmetry of the whole delta prodelta system reflecting prevailing sediment dispersal to the south of each individual delta outlet b the shoreparallel overlapping of successive prodelta lobes fed by distinct river outlets of ever changing relative importance c the delta outlets being artificially forced in a fixed position so that natural avulsion is prevented and delta lobes undergo headland retreat leaving a marked erosion on the prodelta d the presence of prodelta lobes showing widespread bcut and fillq features ranging from 100 to 300 m and depths up to 4 5 m filled with massive silt to very fine sand offshore of short lived very active distributary channels e g po di tolle lobe and suggesting that in some particular interval short lived episodes of submarine erosion are induced by catastrophic increases in river discharge of natural origin or induced by human maintenance the seismic stratigraphy of the modern po delta documents that markedly distinct prodelta architectures form when a newly activated lobe is located updrift north in this case or downdrift south of the one that is retreating in the first case the abandoned lobe becomes sheltered by the new rapidly advancing one in the opposite case the retreating lobe is updrift and a substantial portion of the sediment is cannibalized and transported to the new lobe downdrift d 2005 elsevier b v all rights reserved

geological controls on the geometry of incised valley fills insights from a global dataset of late quaternary examples incised valleys that develop due to relative sea level change are common features of continental shelves and coastal plains assessment of the factors that control the geometry of incised valley fills has hitherto largely relied on conceptual experimental or numerical models else has been grounded on case studies of individual depositional systems here a database driven statistical analysis of 151 late quaternary incised valley fills has been performed the aim being to investigate the geological controls on their geometry results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised valley fills through their effect on the degree and rate of river incision and on river size and mobility the studied incised valley fills developed along active margins are thicker and wider on average than those along passive margins suggesting that tectonic setting exerts a control on the geometry of incised valley fills likely through effects on relative sea level change and river behaviour and in relation to distinct characteristics of basin physiography water discharge and modes of sediment delivery valley fill geometry is positively correlated with the associated drainage basin size confirming the dominant role of water discharge climate is also inferred to exert a potential control on valley fill dimensions possibly through modulations of temperature peak precipitation vegetation and permafrost which would in turn affect water discharge rates of sediment supply and valley margin stability shelves with slope breaks that are currently deeper than 120 m contain incised valley fills that are thicker and wider on average than those hosted on shelves with breaks shallower than 120 m no correlation exists between valley fill thickness and present day coastal prism convexity which is measured as the difference in gradient between lower coastal plains and inner shelves these findings challenge some concepts embedded in sequence stratigraphic thinking and have significant implications for analysis and improved understanding of source to sink sediment route ways and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

architecture of a forced regressive systems tract in the turonian ferron notom delta southern utah u s a abstract the large scale stratigraphic architecture of forced regressive deposits has been documented in many previous studies bed scale facies architectural analyses of these deposits however are still very limited the cretaceous ferron notom delta in southern utah u s a contains a 20 km dip oriented exposure of a stepped forced regressive systems tract the main focus of this paper is to reconstruct the paleogeography and depositional history of the systems tract based on detailed stratigraphic and facies architectural analysis using 23 geological sections photomosaics and walking out of beds internally the systems tract consists of 6 parasequences 11f to 11a from the oldest to the youngest during the progradation of parasequences 11f to 11b the paleoshorelines were wave dominated as indicated by the abundance of hcs and or scs beds wave ripple cross laminated beds and the occurrence of diverse and robust ichnological suites attributable to the skolithos and cruziana ichnofacies progradation of the wave dominated shorelines resulted in more homogeneous and laterally continuous sand bodies from 11b to 11a however there is a distinct change in paleoshoreline regime from wave dominated to tide influenced as indicated by the common occurrence of tidal facies in 11a including 1 lenticular wavy and flaser bedding and bidirectional dipping cross strata 2 reactivation surfaces double mud drapes and ripple cross lamination with opposing dips at the toe of large dune scale cross sets 3 inclined heterolithic strata ihs and sigmoidal bedding with tidal rhythmites and 4 cyclic vertical variation in facies and bed thickness and the common occurrence of sand mud couplets these tide influenced facies show overall lower bioturbation intensity bi 0 3 progradation of the tide influenced shoreline results in more heterolithic delta front facies tidal and or tidal fluvial channels further dissect delta front sandstones forming more isolated sand bodies data from this study as well as previous work show that width and thickness of the forced regressive parasequences are small typically less than 5 km and 20 m respectively in subsurface studies identifying and correlating such small scale parasequences using sparse data involve significant uncertainties a combination of the diagnostic features indicating forced regression and different data sets is essential to better constrain the geometry and architecture these small scale bodies

the quaternary history of the central and southwestern celtic sea abstract the british sector of the celtic sea south of the isles of scilly has recently been investigated by the institute of geological sciences igs using several types of bottom sampler and several types of acoustic device by this means the bathymetry has been improved a surface sediment chart constructed and the stratigraphy established by comparison of boreholes with seismic sections a great deal of new information has emerged regarding the late pliocene quaternary history of the area the celtic sea shelf is very wide with a low general gradient and a relatively deep shelf edge the inner shelf is topographically almost featureless whereas the middle and outer shelf are diversified by a series of large tidal sand ridges tsr running approximately normal to the shelf edge the late pliocene quaternary sediments in the area consist of two main formations the late pliocene early pleistocene upper part of the little sole formation and the late devensian early flandrian melville formation both formations appear to be composed predominantly of sand with subordinate gravel and a minor proportion of mud the upper little sole probably consists mainly of fluvial deposits accompanied by subordinate shallow marine deposits in its upper part whereas the melville consists essentially of tidal deposits which have been fashioned probably by the huthnance mechanism into the tidal sand ridges later erosion has developed a gravelly lag pavement layer b across the top of the melville formation and across exposures of upper little sole or older formations between the ridges above this comes a layer of mobile sandy sediment layer a never more than a few metres thick but fashioned in most places into bedforms appropriate to the local current regime these include ripples megaripples sand waves and sand ribbons ice rafting has evidently been responsible for depositing 1 occasional small mounds of material revealed by side scan sonar which are found on the sea bed between the tsr 2 scattered boulders which occur in the normally pebbly lag pavement and 3 scattered outcrops of till revealed by sampling some of which may represent mounds massive marine planation has occurred in the celtic sea shelf area prior to the upper little sole following the deposition of that formation and probably many times during the pleistocene depths of deposition of samples from the upper little sole together with similar data from the almost coeval st erth beds on the cornish mainland indicate that the area has been tilted oceanwards subsidence of the outer shelf area is confirmed by the relatively deep shell edge the most likely mechanism for these displacements appears to be the resolution of large scale gravity anomalies in the asthenosphere