geomorphic thresholds and complex response of fluvial systems some implications for sequence stratigraphy first generation sequence stratigraphic models have dealt in a very rudimentary fashion with the response of fluvial systems to eustasy a major element of presently accepted models is that rivers incise when sea level falls and aggrade during the ensuing rise well established geomorphic principles state that fluvial systems are complex process response systems that can adjust to internal and external changes in other ways besides incision and aggradation by modifying their stream patterns and channel geometries application of geomorphic principles to sequence stratigraphic models results in the following observations during eustatic lowstands rivers may adjust to lowered base levels and changes in slope by modifying channel patterns therefore not all lowstands produce type 1 sequence boundaries type 1 sequence boundaries characterized by fluvial valley incision are more likely to develop when sea level drops below the shelf slope break resulting in topological relief near the strandline in which headwardly eroding knickpoints form rates of eustatic change although rapid in a geological context are sufficiently low that geomorphic systems can easily maintain their equilibrium during eustatic changes and migrate back and forth across the shelf without major modifications finally und r conditions of relatively static sea level sequences and parasequences of the same scale in time and space as those which form during eustatic change can be deposited as the result of purely intrinsic causes and responses of a fluvial system in general eustasy controls the location of deposition and erosion but the resultant stratal geometry is controlled by sediment supply and processes acting on the sediments as the shoreline moves across the shelf in response to eustasy

climate control on late holocene high energy sedimentation along coasts of the northeastern atlantic ocean abundant sedimentological and geochronological data gathered on european sandy coasts highlight major phases of increased high energy sedimentation in the north atlantic ocean during the late holocene owing to an inconsistent use of the terminology it is often difficult to determine whether studies have described storm built or wave built deposits both deposits can be identified by overall similar coarse grained sedimentary facies but may provide contradictory paleoenvironmental interpretations the aim of this study is to address this issue by analysing a set of published 14c ages recovered from wave built sediment bodies of the pertuis charentais france integration of 14c data highlights seven coarse grained sedimentation pulses csps that reflect a synchronous increase in wave induced sediment supply occurring around 2650 2420 1240 970 800 650 and 450 cal yr b p csps can be matched with geochronological data published on other exposed sandy coasts of the western europe in first order csps were preserved during phases of decreased storm activity and thus limited coastal erosion in the north atlantic ocean from 2700 to 2000 and from 1200 to 600 cal yr b p in second order csps occurred during positive nao and or negative ea wr peaks which are known from previous studies to induce higher waves and to enhance wave induced sediment transport in the pertuis charentais chronological boundaries of csps could be used as a diagnostic tool to differentiate storm deposits indicative of sudden episodic very high energy sedimentation from wave deposits resulting from the sustained action of above average westerly winds blowing across the north atlantic ocean

quaternary compound incised valley in a microtidal environment roussillon continental shelf western gulf of lions france abstract a buried system was observed using seismic data along the northern side of the roussillon coastal plain and inner shelf western gulf of lion mediterranean sea far from the nearest agly and tet rivers it was interpreted as an example of a compound type which is subject to controversy a core 60 meters long was obtained on the sandy beach barrier between sea and lagoon approximately on the axis of the basal surface of erosion mapped from seismic data and long core logs obtained previously on the coastal plain in the lower part of the core 64 m to 26 m b p s l the main estuarine muddy silt facies and thin levels of fluvial gravels intercalated in the mud suggest that successive cycles of base level and sea level falls and rises were recorded this interpretation is confirmed by pollen diagrams showing several successive warming periods during climatic changes differentiated as interglacial phases recorded by the estuarine muds owing to these correlated data we can attest that this incised valley system is of a compound type every vertical succession of fluvial gravels and estuarine muddy silts represents a fundamental depositional sequence typical of the simple model of wave dominated incised valley filling truncated at the top by a subsequent base level fall several depositional sequence remnants are stacked upon each other the chronostratigraphic benchmark is based on microforaminiferal biomarkers which indicate that the time period covered by the successive phases of base level and sea level cycles extends from mis 16 about 600 000 years b p to mis1 present day the exact correlation of base level and sea level cycles with identified climate cycles remains partly approximate but the cycles which contain well known plant associations are quite reliable the internal geometry of the incised valley system based upon high resolution seismic data shows that the lateral migration of the successive phases of incision and filling explains both the preservation of several cycles and the incomplete preservation of the typical facies due to the reworking of the upper part of all individual depositional sequences eustasy is the dominant controlling factor and differential subsidence an important factor on the mid and outer shelf has a reduced impact at this location the preservation of the compound system depends upon the variable maximum depth of erosion reached at each maximum sea level lowstand we propose that different interglacial conditions took place in the drainage basins rather than differences in the lowstand sea level values the transverse shape of the incisions with lateral terraces and deeper channels combined with a continuous lateral shift of the successive incisions also contributed to preservation the lateral shifting is partly due to a normal fault and substratum tilting and partly to the oceanic regime

sedimentary facies and evolution in the qiantang river incised valley eastern china abstract this paper deals with the sedimentary facies and evolution of the qiantang river qr estuary and the characteristics and formation of the incised valley sequences and the related shallow biogenic gas reservoir on the basis of analysis of over 500 cores the result shows that since the last glaciation the late quaternary formation of the qr estuary area underwent three stages 1 deep cutting stage 2 rapid filling stage and 3 burial stage the fall of global sea level during the last glacial maximum enhanced the fluvial gradient and river cutting resulting in the formation of the large scale qr and taihu incised valleys with the interfluve being exposed to air on both flanks of the incised valley fluvial terraces at the elevations are present near the present qr estuarine mouth corresponding to 60 70 90 100 and 115 125 m burial depths the valleys were filled rapidly with fluvial sediments during the post glacial period with the rise of sea level the river mouth migrated to landward and backwater and retrogressive aggradation was enhanced the qr and taihu incised valleys are associated with an early filling and transgressive channel infilling sequence formation and a late filling and transgressive floodplain estuary formation subsequently the qr valley was buried under estuarine marine and estuarine sand bar sediments from bottom to top the incised valley successions can be grouped into four sedimentary facies river channel floodplain estuary estuary shallow marine and estuary sand bar the thickness of the river channel infilling deposits is controlled mainly by base level rising backwater retrogressive aggradation and neotectonism further localized thickening took place where deeper scour pools were present in the incised valley or fluvial terraces were formed during the fall of elative sea level during the deposition of the floodplain estuary facies the conditions of sea level rise tidal regime sediment supply and accommodation space were suitable for the development of a tidal ridge system the sand lenses associated with this facies may represent a tidal ridge system in the incised valley at the later stage when the estuarine sand bars were formed the sedimentary conditions were no longer favourable resulting in absence of sand ridge deposits biogenic gas is stored in the floodplain estuary sand lenses of the incised valleys the changjiang river provides the major sediment supply for the qr estuary sand bar and the qr carried sediments constitute only a small portion of the deposits

the stratigraphic evolution of a large back barrier lagoon system with a non migrating barrier abstract lake st lucia the largest estuarine system in africa is enclosed by a 120 m high compound quaternary barrier dune system in northern kwazulu natal south africa it comprises several discrete sedimentary basins within a single shallow back barrier water body this paper reports the first very high resolution seismic study of the system seven seismic units a g are identified and interpreted based on their geometry acoustic properties and a sediment coring programme the units are bounded by regionally developed sequence boundaries and lower order unconformity surfaces corresponding to bay and tidal ravinement and hiatus surfaces the lowermost subaerial unconformity formed during regression related to late pliocene hinterland uplift initial infilling of this surface in the proximal areas reflects estuarine sedimentation in a mixed wave and tide dominated system during the subsequent lowstand and early transgressive systems tracts overlain by prograding highstand deltaic deposits that developed as sea levels began to stabilise distally this cycle of sedimentation is initially reflected by the infilling of a similar estuarine system that gradually transitioned to a back barrier lagoon superimposed stillstands drove imbalances in the rate of sediment supply and accommodation space and this coupled with the development of an early barrier complex caused lagoon aggradation and shallowing a second similar trend is repeated for the recent postglacial sea level cycle there appears to be no preservation of the intervening pleistocene cycles of erosion and deposition the system is capped by estuarine lacustrine deposits the onset of lower energy estuarine lake conditions began 6235 cal bp in north lake and started earlier in the proximal false bay owing to sheltering by the antecedent barrier of a rocky peninsula this study reveals a markedly different evolutionary history in adjacent basins of the same back barrier system during two full sea level cycles these are attributed to a long established non migrating barrier and to the influence of antecedent conditions on the system response to transgression unlike the us atlantic margin where migrating barriers truncate the infilling sequences the main stratigraphic unconformities within each fill sequence correspond to tidal and bay ravinement surfaces

seaward pinching out and internal stratigraphy of the gironde incised valley on the shelf bay of biscay abstract an incised paleovalley offshore the estuary mouth of the gironde river southwest france was evidenced recently comptes rendus de l academie des sciences de paris 326 1998 701 nevertheless its seaward extension to the shelf break was still unknown new high resolution geophysical data were acquired on the continental shelf in order to follow the incision until the shelf break after processing the seismic lines the shape of the valley was identified and the valley fill in terms of sequence stratigraphy was interpreted the valley fill contains a single sequence corresponding to a fifth order cycle 20 kyr the three systems tracks described onshore by allen and posamentier journal of sedimentary petrology 63 1993 378 sepm society for sedimentary geology special publication tulsa 1994 225 are present offshore the lowstand is poorly developed and is only present in the proximal part of the incised valley the transgressive systems tract tst constitutes the bulk of the valley fill it is composed of landward prograding estuarine clinoforms in the distal part of the valley early tst phase 1 and of landward migrating tidal inlet fill deposits in the proximal part of the valley late tst phase 2 the thin early highstand systems tracts hst strata downlap seaward onto the maximum flooding surface and caps the tst as expected in this wave and tide dominated environment the tidal and wave ravinement surfaces which bound the tst are particularly well developed the valley incision tapers 50 km offshore of the estuary mouth the depth of the basal sequence boundary gradually decreases seaward and is locally truncated by the wave ravinement surface around 70 m below the mean sea level these observations indicate that during the lowstand times rivers do not always generate continuous cross shelf incised valleys they may adjust to a rapid drop in base level by modifying their channel morphology i e deep large channels located upstream change downstream to shallow anastomosed channels with a weaker erosional ability therefore the lowstand fluvial channels will be poorly developed and will eventually died out in the proximal part of the shelf because they are unable to keep pace with a phase of rapid sea level drop similar observations have already been reported for the english channel paleoriver geological society special publication london 1996 203 these de geologie marine universite de bordeaux 1 1997 265

the influence of limited accommodation space on the stratigraphy of an incised valley succession weiti river estuary new zealand abstract the influence of limited accommodation space on estuarine stratigraphy was investigated using vibrocores from the weiti river estuary a narrow fault control estuary of the north island new zealand the weiti incised valley fill comprises eight lithofacies arranged into two distinct depocentres separated by the main estuary channel the seaward depocentre is occupied by a marine influenced sand accumulation consisting of transgressive to highstand open bay deposits overlain by regressive tidal flat and shelly beach ridge deposits the landward depocentre is dominated by a tidal fluvial transgressive to highstand bay head delta complex that includes point bar channel lag and saltmarsh deposits radiocarbon ages for in situ shell and organics are used to establish the chronology of valley filling holocene marine deposition commenced late in the transgression ca 8 ka bp and was dominated by an open bay depositional environment in the seaward depocentre and by a tidal point bar within the landward depocentre at the time of maximum transgression ca 6 5 ka bp most of the valley fill was in place highstand deposition has been characterised by formation of seven shelly beach ridges and vertical accretion of tidal flats in the seaward depocentre and pointbar accretion to supratidal levels in the landward depocentre the organization of transgressive and highstand deposits in the weiti river estuary has been strongly influenced by limited accommodation space to the extent that i marine flooding of the seaward depocentre was delayed due to a fluvial terrace at the present day estuary mouth thereby preventing formation of a continuous transgressive bay head delta ii the low wave environment at the sheltered estuary mouth was suitable for barrier beach ridge construction only when accretion had bought the valley floor to within wave base during stillstand and iii the narrow valley has promoted channelization of tidal and river flow which coupled with the lack of a barrier prevented a central basin environment forming and caused the highstand bay head delta to develop in a restricted area despite these limitations on morphological and stratigraphical development the weiti river estuary has formed an overall transgressive to regressive depositional succession that is broadly consistent with idealized models of incised valley stratigraphy

outer to inner shelf response to stepped sea level rise insights from incised valleys and submerged shorelines abstract shorelines respond to rising sea level through processes such as erosion landward migration and in situ drowning i e overstepping submerged and preserved shorelines on the continental shelf play a key role in examining coastal response to rising sea levels as they provide important information on how modern shorelines may evolve in time and space within the context of changing climate and post glacial sea level rise this study identifies and assesses the response of a continental shelf to stepped rises in sea level with particular focus on the stepwise evolution of incised valleys and shorelines from the shelf edge to the inner shelf multibeam bathymetry from the mid outer allows for the analysis of seafloor morphology including the protea banks reef a palaeo shoreline complex and the adjacent incised sediment starved continental shelf six seismic units and intervening surfaces are identified using interpretations from sub bottom profiles these include the incised acoustic basement variable incised valley fill successions aeolianite ridges and post transgressive shoreface and associated sediments that withstood wave ravinement processes the incised valleys of the outer shelf are manifested as distinctive seafloor depressions filled at their bases by fluvial deposits overlain in the unfilled valley by deposits derived from cascading subaqueous dunes which comprise the upper most post transgressive sediments a core intersecting the dune material yields a maximum age of deposition of 1191 1263 cal yr bp 68 range synchronous with a period of higher than present sea levels in the region suggesting reworking and redistribution of coastal sediment as shelf sediment post transgression during the stepped rises in sea level the shoreface has disconnected from the contemporary shoreline and is preserved by means of topographic barriers formed by antecedent topography as relict shoreface deposits we provide a new perspective of shoreline response to stepped rises in sea level by integrating the seismic architecture of incised valley fills and shorelines across the continental shelf thus allowing for the assessment of variation in rates of relative sea level rise since the last glacial maximum

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

palaeo drainage incised valley fills and transgressive systems tract sedimentation of the northern kwazulu natal continental shelf south africa sw indian ocean abstract two sequence boundaries are recognised in seismic data collected from the narrow northern kwazulu natal continental shelf these correspond to late cretaceous and latest pleistocene last glacial maximum lgm periods of sea level fall where fluvial incision into the shelf resulted in several incised valleys having formed in both examples the ensuing transgressive valley fills document an evolution from fluvially dominant sedimentation to classic backbarrier estuarine conditions central estuary basin sedimentation is most prominent within each fill and is separated from the underlying fluvial sediments by bayline ravinement processes tidal ravinement surfaces separate the upper estuarine sequences from barrier and shoreface deposition most easily observed in the latest pleistocene holocene valley fills where a holocene unconsolidated sediment wedge overlies the estuarine fill the wedge itself is characterised by two packages of sediment separated by a regionally occurring wave shoreface transgressive ravinement surface which crops out as a semi indurated shell hash in the mid to outer shelf late cretaceous examples are capped by deposits exhibiting oblique parallel to wavy reflectors interpreted as increasingly energetic deposits analogous to flood tide deltaic sedimentation valley incision and fill are linked to two onshore coastal lake systems lake sibaya and lake st lucia and appear to be the product of barrier breaching and fluvial re adjustment to baseline shifting of these systems during forced regression lake st lucia exhibits a composite palaeo drainage channel where both sequence boundaries merge within the lake margins lake sibaya has two distinct palaeo channels for each sequence boundary episode a late cretaceous channel which fed a small incised valley within which a modern day submarine canyon is located the other an lgm channel directed in towards the head of wright canyon the subsequent input of sediment causing this canyon to breach furthest into the shelf than any other canyon in the area offshore of lake st lucia the most proximal portions of the associated leven canyon occupy the mid shelf and are underlain by lake st lucia palaeo drainage channels of lgm age where erosion along the initial lgm palaeo channel has occurred freshwater exchange between the shelf and the fringing lake system has resulted in the development of sinuous features of leven canyon which have eroded in a downslope fluvial like manner thus occupying palaeo drainage lows as erosive flows were entrained models proposed here indicate that 1 the limited accommodation space offered by a narrow continental shelf may allow for a greater preservation potential of wave dominated estuarine facies 2 the seismic expression of these fills may vary yet still satisfy similar sedimentological conditions and 3 antecedent valley topography increases the preservation potential of these valley fills by providing a preferred space in which to re incise and then fill during sea level rise

an experimental study of the effects of base level change on fluvial coastal plain and shelf systems abstract several of the concepts of sequence stratigraphic models were tested by experiments in a large flume using different gradients for successive runs a physical model of a fluvial drainage basin coastal plain continental shelf and continental slope was constructed in all experiments initial gradients of the coastal plain and shelf were identical systematic raising and lowering of the water surface simulated the changes in relative sea level i e base level that are similar to most sequence stratigraphic models base level changes significantly affected the shelf area but they had little effect on the fluvial drainage basin during base level falls fluvio deltaic progradation occurred fluvial aggradation occurred only during periods of base level stillstand or rise because of the slow rate of head ward erosion of incised valleys a significant time gap existed from the time base level first fell below the shelfbreak and the development of a cross shelf bypass valley during this lag time deposition occurred on the exposed shelf to form a fluvial braid plain concurrently channels developed at the shelfbreak and grew by headward erosion at various rates continuous incision and widening of these channels formed valleys these valleys were not linked directly to the main drainage basin unt l ultimately one captured the flow from that drainage at that point other valleys were abandoned and ceased to grow during the subsequent base level rise the single large cross shelf valley filled with coarser sediments while the other valleys partially filled with finer suspended load sediments the main cross shelf valley also supplied coarser sediments to the slope

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

comparison of basin morphometry analyses derived from different dems on two drainage basins in turkey morphometric analyses provide important data about basins and their drainage networks many data sources which are produced from different techniques can be used in this analysis two areas which have similar areal and formal features but have different vegetation density were selected as study areas kabisre and koyunluyusufozu basin selected parameters were implemented to both basins using five different datasets aster gdem srtm dem alos dsm 30 m and topo dems 30 m and 10 m the topo dems were produced from 1 25 000 scaled digitized topographical maps the morphometric analyses result of topo dems 10 m resolution was used as the benchmark data for comparing the results of the other data sources as a result srtm dems gave the most compatible results with the results of reference data for the study area of kabisre basin that has heavy vegetation and the alos dsms gave the closest results to the reference data in study area on koyunluyusufozu basin that is deprived of vegetation

morphological evolution and time varying bedrock control of main channel at a mixed energy tidal inlet maumusson inlet france abstract maumusson inlet located on the french atlantic coast connects the atlantic ocean with the marennes oleron tidal bay the tidal range 2 6 m and wave climate mean height 1 5 m place this tidal inlet in the mixed energy tide dominant category of hayes 1979 barrier island morphology in leatherman s p ed barrier island academic press new york pp 1 28 an innovative method combining high quality bathymetric data nine accurate digital elevation models since 1824 with a very high seismic resolution demonstrates a major tidal inlet evolution from 1824 onwards and its dramatic acceleration since 1970 the chronology of those morphological changes suggests strong coupling between the location of the tidal channel and the behaviour of the adjacent shorelines the recent shoaling and migration of the inlet channel can be attributed to a decrease in tidal prism due to the filling in sediment of marennes oleron bay seismic data give evidence that the inlet was located on a major incision of the bedrock it can be inferred that the bedrock exerts control of channel location this control varying in time as a function of channel depth a conceptual model is proposed including the inlet its adjacent shorelines the tidal bay and the time varying bedrock control of main channel location such a model could be considered valid in similar cases along other coastlines i e coastlines with a fine unconsolidated sediment sheet

spatially explicit bathymetric reconstruction from lead line depth soundings of the late 17th century abstract sequences of repeated bathymetric surveys through time have been successfully used to document the morphodynamical evolution of coastal environments within historical times most chronobathymetric sequences have a restricted temporal coverage as surveys rarely date back earlier than the 19th century the aim of this study is to explore the potential of older lead line depth measurements as a reliable source of bathymetric data a late 17th century marine chart of the pertuis charentais france was used as a test case high resolution scans of the chart sheets were retrieved from a public online digital library a rare manuscript contemporary to the chart was obtained from the french national archives in order to constrain the methodology used to acquire depth measurements a spatially explicit bathymetry covering 1500 km2 was reconstructed from the interpolation of about 4600 georeferenced depth soundings vertical error was estimated by assuming the equivalence of depth values between the late 17th century and the recent 1960 bathymetries above subtidal rocks outcropping on the seafloor documentary data indicated that the chart author did not acquire depth measurements on purpose but instead collected data taken by local sailors and coasting pilots over an unknown period of time probably ranging from a few years to a few decades the large vertical error estimated to 4 5 m mainly resulted from the lack of tide correction bathymetric difference maps could not be computed but despite these weaknesses the large scale sediment infilling of the area and the long term evolution of an estuarine sandbank could be documented in agreement with previous works beyond its utility for local studies this article provides insights into the processing of depth measurements acquired long before modern hydrography surveys and demonstrates that such old marine charts deserve consideration provided conditions are met for their critical assessment

origin and morphosedimentary evolution of fine grained modern continental shelf deposits the gironde mud fields bay of biscay france the gironde mud fields are thin blankets 4 m that extend from the inner to mid shelf over a restricted area 600 km 2 and overlie palimpsest sands and gravels seaward of the modern gironde estuary south western france the bulk of the mud has accumulated over the last two millennia and reflects the complex interactions of 1 an increasing estuarine supply of suspended particulate matter 2 resuspension of substrate material by storm events and 3 biological mixing the combination of these processes has produced various features within the deposits related to 1 the water depth and distance from source of the fine grained material which are manifested as a proximal distal cross shelf trend from an area of alternating mud sedimentation temporary after large river flows with resuspension by storm events to an area of mud accumulation in deeper water where bioturbation predominates 2 expansions of the mud depocentres over time such that they become more remote from sources of coarser shelf sediment resulting in an upward fining trend the lithofacies of the gironde shelf mud fields exhibit a number of similarities to those of larger scale modern muddy shelves and ancient shallow water mudrocks this work provides a detailed description of a facies model for fine grained shelf sediments deposited under relatively constant sea level

transgressive systems tract of a ria type estuary the late holocene vilaine river drowned valley france the understanding of control parameters of estuarine infilling at different scales in time and space is important for near future projections and better management of these areas facing sea level change during the last 20 years the stratigraphy of late quaternary estuaries has been extensively investigated leading to the development of depositional models which describe the sedimentary facies distribution according to changes in sea level tidal range and wave activity but few of them describe in detail the influence of the estuarine geomorphology on the atlantic coast recent studies provide a detailed understanding of the sedimentary infill succession of incised valleys during the late holocene transgression with recent emphasis on the macrotidal bay of the vilaine river in south brittany the latter has shown the importance of the inherited morphology in controlling the preservation of the sedimentary deposits however until now there has been little information available on the geometry of the underlying bedrock of the estuary and its immediate approaches including the holocene history of the most proximal part of the vilaine river estuary the recent acquisition of very high resolution seismic reflection chirp and sediment core data in the vilaine estuary provides the opportunity to address several of these issues leading to the identification of the controlling factors that played a role in the sedimentary filling of the estuary the estuary of the vilaine river is one of the most sheltered estuaries of the atlantic coast and thus shows an excellent record of the successive transgressive phases since the last glacial period the valley of this ria type estuary is incised in the hercynian magmatic and metamorphic rocks of the armorican massif along the striking branches of the south armorican shear zone and filled with well stratified sediments the study of the morphology of the substratum in the estuary reveals narrow paleovalleys 1 km wide with a maximum depth of 20 m the shapes and dimensions of these paleovalleys are comparable with those observed upstream in the present day vilaine river valley facies analysis of seismic and sedimentary data complemented by 21 ams radiocarbon age dating enables the reconstruction of the infilling of the estuarine valley the valley is filled by pleistocene to early holocene alluvial coarse grained pebbly sands overlain by mid to late holocene marine sands silts and muds from 10 000 to 5000 cal bp the marine transgression shows a rapid initial phase of transgression followed by a progressive slowing down which can be recognised over more than 90 km in an upstream direction the rapid transgression developed homogeneously over the entire length of the estuary with a widespread expression of tidal currents tide dominated estuary the slow phase of the transgression gives rise to a differentiated expression of the hydrodynamic factors according to the geomorphological setting the sedimentary deposits of the innermost and narrow part of the estuary reflect a strong control of tidal and river currents when the influence of tidal currents increases at the expense of fluvial control in a downstream direction the sedimentary filling of the outer reaches of estuary shows a strong influence of tidal currents modulated by changes in sea level where from 5700 to 3000 cal bp the progressive decrease in accommodation space promotes the expression of wave action wave dominated estuary finally from 5000 years bp to present day the stabilisation of sea level gives birth to scour and lag sedimentary morphologies scour and lag estuary the sedimentary record appears thus strongly marked by the holocene transgression and the geomorphological setting where hydrodynamic parameters superimposed on the geomorphological and eustatic contexts expressed in different ways in time and space govern the evolution of the estuarine system

geological inheritance and its role in the geomorphological and sedimentological evolution of bedrock hosted incised valleys lake st lucia south africa abstract the morphology of lake st lucia africa s largest estuary has been strongly influenced by antecedent topography throughout its quaternary evolution the 5 20 km southern basin is bounded to landward by a 50 m high early mid pleistocene dune ridge and to seaward by a 100 m high late pleistocene holocene dune barrier nine seismic units a i are identified in the enclosed basin along with two regionally developed sequence boundaries sb1 and sb2 and two tidal ravinement surfaces trs1 and trs2 the lowermost sequence boundary sb1 is related to regional late pliocene hinterland uplift sb2 is related to the last glacial maximum lgm when sea levels fell 130 m below present lowstand fluvial sediments occupy the base of both sb1 and sb2 incisions thick central basin deposits dominate the valley fills more so in the pliocene age valleys the occurrence and thickness of which is attributed to sheltering by a seaward barrier dune system as well as to the low gradient settings prograding tidal bedforms occupy the minor incisions formed within the tidal ravinement surfaces marking the onset of lagoonal conditions in the area the system is capped by lagoonal deposits deposited above tidal flats a series of prograding spits mark the early stages of lagoonal segmentation in the holocene the preservation of only one incision and fill sequence prior to the development of an lgm aged valley succession is attributed to geological inheritance whereby older valleys were repeatedly re incised by younger valleys throughout the pleistocene causing partial preservation of pleistocene fills up to the most recent cycle the older fill remnant relates to a larger magnitude base level fall prior to the quaternary which survived erosion during subsequent sea level falls adjacent topography in the form of rocky cliffs and the seaward fronting barrier limit the accommodation space in which infilling material can be hosted outside the major valley network the competent basement rock into which these valleys have incised protected lowstand fluvial sediments from subsequent tidal ravinement

detailed architecture of a compound incised valley system and correlation with forced regressive wedges example of late quaternary tet and agly rivers western gulf of lions mediterranean sea france abstract quaternary incised valley systems are usually characterized by the preservation of a single valley fill attributed to the last post glacial period moreover there are very few cases of correlation between incised valley system developed on inner shelf and sedimentary units observed on the mid to outer shelf mainly forced regressive wedges the roussillon shelf in the western part of the gulf of lion is a particular example of preserved quaternary compound incised valley system also characterized by a direct correlation with the forced regressive lowstand wedges on the mid outer shelf high resolution seismic data and a borehole 60 m deep located on the beach barrier permit an accurate study of the geometry and lithology of the system six imbricated and more or less preserved incised valleys and valley fills are observed up to the inner to mid shelf the key surfaces associated to the incised valleys are correlated to the boundaries of the forced regressive wedges they are assumed to be reworked surfaces at the borehole location only few thin layers less than 1 m thick of coarse grain and or floating pebbles are observed and should correspond to preserved fluvial lowstand deposits reworked under marine influence the valley fills are mainly composed of estuarine muddy silts from ams 14c age dating it is inferred that the uppermost incised valley system is younger than 45 ky cal bp based on those observations the six preserved incised valley systems are assumed to be controlled by the last six 4th order sea level cycles 100 ky of the middle to late quaternary the paleo topography of the underlying plio quaternary deposits controls the compound incised valley system location the deep topography of the messinian erosionnal surface is a controlling factor at a lower degree the partial preservation of the successive valley fill is attributed not only to the differential subsidence but also to the lateral migration of each incision and to the hydrodynamic regime

seismic stratigraphy of the gulf of cadiz continental shelf a model for late quaternary very high resolution sequence stratigraphy and response to sea level fall

how and where do incised valleys form if sea level remains above the shelf edge sequence stratigraphic models predict that during relative sea level fall rivers will cut incised valleys across the exposed continental shelf incision is driven by the exposure of convex up topography and consequent downstream increases in stream power modern shelf profiles from passive margin and foreland basin settings show that profile convexities occur at the shelf edge and at the current highstand coastline the coastal prism in nonglacial times which form much of earth9s history it is unlikely that the shelf edge was subaerially exposed during such periods patterns of incision would have been primarily determined by the shape of the coastal prism on the basis of modern shelf profiles from passive margin and foreland basin settings river incision of as much as 20 to 70 m would be centered upon the preceding highstand coastline and would be restricted to the inner part of the shelf deeper incised valleys would only result from exposure of the shelf edge or from the processes involved in the formation of submarine canyons

evolution of an incised valley coastal plain estuary under low sediment supply a give up estuary the literature on incised river valley sedimentology is dominated by studies of sediment rich systems in which the valley has been filled during and or shortly after drowning in contrast the holocene evolution of the kosi lagoon south africa an incised coastal plain river valley took place under very low sedimentation rates which have produced a distinctive stratigraphy and contemporary sedimentary environments the findings are based on a synthesis of the results of studies of seismic stratigraphy sediment distribution morphodynamics and geomorphology barrier migration was prevented by a high pre holocene dune barrier against which holocene coastal deposits accumulated in an aggradational sequence holocene evolution of the back barrier involved i drowning of the incised valley ii wave induced modification of the back barrier shoreline leading to segmentation during the highstand and iii marine sedimentation adjacent to the tidal inlet segmentation has divided the estuary into a series of geochemically and sedimentologically distinctive basins connected by channels in the estuarine barriers the seismic stratigraphy of the back barrier essentially lacks a transgressive systems tract shoreline modification and deposition having been accomplished during the highstand the lack of historical geomorphological change suggests that the system has achieved morphological equilibrium with ambient energy conditions and low sediment supply this study presents a classification for estuarine incised valley fills based on the balance between sea level rise and sedimentation in which kosi represents a give up estuary where much of the relict incised channel form is drowned and preserved it exhibits a fundamentally different set of evolutionary processes and stratigraphic sequences to those of the better known incised valley systems in which sedimentation either keeps pace with sea level keep up estuaries or occurs after initial drowning catch up estuaries

complex proximal deposition during the plinian eruptions of 1912 at novarupta alaska proximal 3 km deposits from episodes ii and iii of the 60 h long novarupta 1912 eruption exhibit a very complex stratigraphy the result of at least four transport regimes and diverse depositional mechanisms they contrast with the relatively simple stratigraphy and inferred emplacement mechanisms for the previously documented better known medial distal fall deposits and the valley of ten thousand smokes ignimbrite the proximal products include alternations and mixtures of both locally and regionally dispersed fall ejecta and numerous thin complex deposits of pyroclastic density currents pdcs with no regional analogs the locally dispersed component of the fall deposits forms sector confined wedges of material whose thicknesses halve radially from and concentrically about the vent over distances of 100 300 m cf several kilometers for the medial distal fall deposits this locally dispersed fall material and many of the associated pdc deposits is rich in andesitic and banded pumices and richer in shallow derived wall rock lithics in comparison with the coeval medial fall units of almost entirely dacitic composition there are no marked contrasts in grain size in the near vent deposits however between locally and widely dispersed beds and all samples of the proximal fall deposits plot as a simple continuation of grain size trends for medial distal samples associated pdc deposits form a spectrum of facies from fines poor avalanched beds through thin bedded landscape mantling beds to channelized lobes of pumice block rich ignimbrite the origins of the novarupta near vent deposits are considered within a spectrum of four transport regimes 1 sustained buoyant plume 2 fountaining with co current flow 3 fountaining with counter current flow and 4 direct lateral ejection the novarupta deposits suggest a model where buoyant stable regime 1 plumes characterized most of episodes ii and iii but were accompanied by transient and variable partitioning of clasts into the other three regimes only one short period of vent blockage and cessation of the plinian plume occurred separating episodes ii and iii which was followed by a single pdc interpreted as an overpressured blast involving direct lateral ejection in contrast regimes 2 and 3 were reflected by spasmodic sedimentation from the margins of the jet and perhaps lower plume which were being strongly affected by short lived instabilities these instabilities in turn are inferred to be associated with heterogeneities in the mixture of gas and pyroclasts emerging from the vent of the parameters that control explosive eruptive behavior only such sudden and asymmetrical changes in the particle concentration could operate on time scales sufficiently short to explain the rapid changes in the proximal 1912 products

the georgia embayment continental shelf stratigraphy of a submergence forty vibracores taken across the continental shelf and in proposed drilling lease areas of the southeast georgia embayment are used to document the unconsolidated shelf sediment cover the holocene pleistocene sediment veneer is thin generally less than 4 m thick lagoon sediments deposited during the last regression shelf emergence or the holocene transgression shelf submergence occur in patches on the inner and central shelf because essentially only late pleistocene and holocene mollusk shells are present in the shelf sediment cover it is believed that most of the carbonate fraction was removed by subaerial leaching during low sea level stands aided by mechanical abrasion and biological degradation during the regressive transgressive cycle during each transgression or submergence the surficial sand sheet is recharged with a new biogenic carbonate fraction along with the addition of small amounts of clastic sediments derived from overrun estuaries and erosion of underlying tertiary sediments the stratigraphy based on the vibracores supports the concept of cross shelf migration of the shore face barrier island systems in response to rising sea level sedimentologic and paleontologic analyses also indicate that extensive in place mixing of shelf sediments may have occurred an important factor to consider in evaluation of the fate of particulate pollutants the establishment of the time frame of such mixing should be given high priority in future studies

formation and preservation of an overstepped segmented lagoon complex on a high energy continental shelf the duration of shoreline occupation at a given sea level coastal response to sea level change and the controls on preservation of various shoreline elements can be recognized by detailed examination of submerged shorelines on the continental shelf using bathymetric and seismic observations this article documents the evolution and preservation of an incised valley and lithified barrier complex between 65 m and 50 m mean sea level on a wave dominated continental shelf the barrier complex is preserved as a series of aeolianite or beachrock ridges backed by laterally extensive back barrier sediments the ridges include prograded cuspate lagoonal shoreline features similar to those found in contemporary lagoons the incised valley trends shore parallel behind the barrier complex and records an early phase of valley filling followed by a phase of extensive lagoonal sedimentation beyond the margins of the incised bedrock valley sea level stability at the outer barrier position ca 65 m enabled accumulation of a substantial coastal barrier that remained intact during a phase of subsequent slow sea level rise to 58 m when the lagoon formed these lagoonal sediments are stripped seawards by bay ravinement processes which caused the formation of several prograded marginal cuspate features an abrupt rise in sea level to 40 m correlated with melt water pulse 1b enabled the preservation of thick lagoonal sediments at the top of the incised valley fill and preservation on the sea bed of the cemented core of the barriers this situation is unique to subtropical coastlines where early diagenesis is possible the overlying sandy sediment from the uncemented upper portion of the barriers is dispersed by ravinement partly burying the ridges and protecting the underlying sediments the high degree of barrier or shoreline preservation is attributed to rapid overstepping of the shoreline early cementation in favourable climatic conditions and the protection of the barrier cores by sand sheet draping

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

tidal deposition systems of china s continental shelf with special reference to the eastern bohai sea abstract the continental shelf of china has undergone a large scale marine transgression tidal currents have become the main active agent and have had a profound influence on the deposition and geomorphology of the shelf the continental shelf of china has five modern tidal deposition systems 1 the eastern part of the yellow sea 2 the eastern part of the bohai sea 3 off the mouth of yangtze river 4 to the west of taiwan and 5 the strait of qiongzhou when the tidal current speed is above 150 cm s erosion dominates and reciprocating currents form deep scour furrows when the tidal current speed is 50 to 150 cm s deposition is dominant and tidal currents form tidal shoals i e tidal sand ridges and tidal sand sheets whose margins are near an absolute ellipticity value for the m2 tidal component of 0 4 when the absolute m2 value is less than 0 4 a reciprocating current is strong enough to form tidal sand ridges when the absolute value is above 0 4 a rotating current increases so as to form a tidal sand sheet tidal deposition material came mainly from tidal erosion and locally redeposition of late pleistocene sediments and from the neighbouring sea bottom the tidal deposition system in the eastern bohai sea is a typical example it consists of the laotieshan channel scour furrow the liaodong shoal sand ridges and the bozhong shoal sand sheet the maximum tidal current speed in the laotieshan channel where strong erosion occurs is up to 250 cm s in the liaodong shoal the maximum tidal current speed is 64 115 cm s and the absolute ellipticity value of the m2 tidal component is less than 0 4 in the bozhong shoal the maximum tidal speed is 58 79 cm s and the absolute ellipticity value of the m2 tidal component is above 0 4 the small scale bedforms surveyed in detail in the area show that the sand ridges and sand sheet are still under the action of tidal current processes at the present time based on the interpretation of tidal currents bedforms and sediment thickness it is inferred that the general direction of sediment transport within the study area is nnw from the laotieshan channel to the liaodong and bozhong shoals the small scale bedforms in the detailed survey area indicate a local net sediment transport from south to north

spatial and temporal variations in incised valley systems from the durban continental shelf kwazulu natal south africa abstract the evolution of several incised valley systems from the kwazulu natal shelf is compared over time these represent the shelf extension of the collective durban harbour drainage system and the mgeni mhlanga and mdloti rivers two main ages of incision are apparent early santonian cretaceous and late pleistocene holocene the early valleys formed by tectonic controls namely phases of higher frequency base level fall superimposed on lower frequency higher order transgression the results are complex networks of stacked compound valleys that have been exploited by some of the younger networks formed by glacio eustatic fall prior to the last glacial maximum lgm of 18 ka bp the valley fills have evolved from high energy basal fluvial deposits low energy central basin fines mixed energy estuarine mouth plug deposits clay rich flood deposits through capping sandy shoreface deposits the earliest fills are dominated by central basin deposits and were underfilled as a result of low gradient and limited sediment supply the more recent late pleistocene holocene fills have significantly thicker fluvial deposits as a result of increased gradient and stream competence during the later stages of valley and shelf evolution the youngest valleys show a situation of differential evolution along the valley length due to varying rates of sea level rise in the holocene initial rapid sea level rise caused drowning and overstepping of the outer segment of the incised valley whereas slower rates of sea level rise in the late holocene caused shoreface ravinement of the inner mid segments of the valley this differential exposure to accommodation has resulted in a sedimentological partitioning between tide dominated facies in the outer valley segment and river dominated facies in the inner segment cf cooper 2001

contrasting sediment records of marine submersion events related to wave exposure southwest france abstract sediment records of two contrasting backshore coastal marshes extremely vulnerable to recent and historical marine flooding events located on the sw coast of france have been investigated using a multiproxy approach the studied marshes are 30 km apart and have been flooded by similar storm events 7 marine floods in the last 250 years one is located in a wave exposed coast but isolated from the sea by a sediment barrier whereas the other is located in a sheltered estuarine environment and isolated from the sea by a dike one core was collected in each marsh and information on grain size foraminifera shell contents and stable carbon isotopes was obtained along with an age model using 210 pb 137 cs and 14 c core data combined with historical maps give evidence of a typical estuarine backfilling part of the holocene regressive parasequence including an intertidal mudflat at the base and a backshore environment at the top despite the absence of grain size anomalies marine flood related sedimentation in the backshore area of both marshes is identified by a mixture of marine and terrestrial features including marine fauna vegetation debris and variation in the 13 c signature of the organic fraction very low sedimentation rates between flood events and or bioturbation prevents the identification of individual episodic marine floods in the sediment succession comparison of the two sedimentary successions shows that the foraminifera deposited by marine submersions are of two different types foraminifera are monospecific and originate from the upper tidal mudflat in the sheltered marsh whereas in the backshore marsh located in a wave exposed environment they show higher diversity and originate from both shallow and deeper water marine environments this study shows that wave exposure can control the faunal content of marine flood sediment records in coastal marshes

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 and morphology of the outer segment of a mixed tide and wave dominated incised valley revealed by hr seismic reflection profiling the paleo charente river france abstract we present new single channel high resolution seismic reflection profiles ground truthed by vibrocore data dedicated to the outer segment of an incised valley connected to the charente river french atlantic coast the present day charente is located about 50 km northward of the well known gironde estuary those river mouths are comparable in terms of marine hydrodynamic parameters but strongly differ by their water discharge and catchment area seismic data are processed and interpreted to develop a three dimensional seismic stratigraphic framework for the charente incised valley fill the channel network of the drowned charente valley is evidenced for the first time and shows a seaward distributary pattern which is likely influenced by neotectonic control incision depth and width of the charente and gironde incised valleys are similar supporting the idea that correlation between valley width and modern hydrology is poor the internal geometry of the charente valley fill shows in seismic lines high to middle angle dipping reflectors at the base and a top of sequence with an intervening low angle seismic unit this pattern is associated with a landward migration of the seismic unit depocentres sedimentary facies of the main seismic units suggests an upward and landward shift from estuarine mixed sands and muds to estuary mouth massive sands topped by fine marine sands the described sedimentary and seismic characters and the holocene age of the valley fill near the present day charente river mouth suggest that the drowned charente valley infill mainly corresponds to a single transgressive sequence emplaced during the last sea level rise beyond the local interest the dense seismic grid recorded across the charente drowned valley gives a seismic validation for the model of large valley fill proposed by ashley and sheridan ashley g m sheridan r e 1994 depositional model for valley fills on a passive continental margin in r w dalrymple r j boyd b a zaitlin eds incised valley systems origin and sedimentary sequences sepm soc sediment geol spec publ tulsa vol 51 pp 285 301 we propose that high low high internal reflection pattern succession represents the seismic sandwich in reference to the ashley and sheridan ashley g m sheridan r e 1994 depositional model for valley fills on a passive continental margin in r w dalrymple r j boyd b a zaitlin eds incised valley systems origin and sedimentary sequences sepm soc sediment geol spec publ tulsa vol 51 pp 285 301 sedimentary sandwich such seismic pattern is also recognized in the gironde valley mar geol 175 2001 183

eustatic and tectonic control on deposition and lateral variability of quaternary regressive sequences in the adriatic basin italy abstract during the late pleistocene sea level variations related to glacio eustatic cycles induced the deposition of four regressive sequences on the western continental shelf of the adriatic basin the four sequences are bounded by erosion surfaces that formed during sea level fall sub aerial exposure of the shelf and subsequent sea level rise and erosional reworking the sequences and the erosion surfaces at their top numbered 1 4 top down are correlated on distances in the order of 300 km in the central and south adriatic core control on deposits of the most recent depositional sequence sequence 1 suggests that each sequence records a fourth order ca 100 120 kyr cyclicity of sea level change within each depositional sequence progradational units representing highstand to forced regression are dominant whereas transgressive deposits are absent or reduced in both thickness and lateral extent sequences are thus referred to as regressive sequences deposition during sea level fall occurred on an overall subsiding shelf through the dispersal of fine grained sediment supplied from the adjacent alpine and apennine chains this resulted in stacked forced regression deposits thick enough to survive complete removal during subsequent phases of sub aerial and marine erosion erosion and or non deposition were enhanced only where tectonic uplift and morphological highs further reduced the remaining accommodation space resulting in local thickness reduction or in the non preservation of the regressive sequences at larger scale thickness variability and depocenter distribution north and south of the gargano promontory an uplifted block bisecting the adriatic foreland reflect differential deposition and preservation of regressive deposits as a function of contrasting tectonic setting and resulting physiography of the shelf and upper slope

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

compound incised valley characterization by high resolution seismics in a wave dominated setting example of the aude and orb rivers languedoc inner shelf gulf of lion france a branch of a time calibrated late quaternary compound incised valley complex is investigated using high and very high resolution seismic data the incised valley system is confined on the inner shelf and entrenched parallel to the shore in unconsolidated pliocene deposits the infilling of the incised valley system comprises three sigmoidal bodies dipping progressively downstream representing depositional sequences the lowermost sequences are less well preserved at their downstream extremity and the whole system is both aggrading and prograding older pleistocene late quaternary sequences could be preserved under the coastal plain individual sequences are closely similar to the classic model of a microtidal incised valley fill nevertheless the central estuary bay basin muds are seen to interfinger locally with high energy deposits that represent potential reservoirs the properties prograding and aggrading architecture and occurrence of high energy deposits and preservation of these compound incised valley fill deposits are attributed to general glacio eustatic cycles and local atmospheric and oceanic regime and proximity of the hinge line conditions data acquisition strategy is a determining factor to interpret such systems

multi time scale evolution of a wide estuary linear sandbank the longe de boyard on the french atlantic coast abstract this trans disciplinary work combines modeling and observational approaches and offers a unique dataset to study the behaviour of a wide estuary linear sandbank over different time scales the sandbank studied the longe de boyard lies in a macrotidal estuary environment off the french atlantic coast side scan sonar data combined with shipek grab samples and numerical modeling of waves and tides revealed its short term dynamics historical 1824 and present day 2000 and 2003 bathymetric data combined with numerical simulations of waves and tides and tide related sand transport in 1824 and seismic profiling were then used to demonstrate the long term evolution of the sandbank and how this correlates with the short term dynamics the geological evolution centuries to millennia was finally deduced from seismic stratigraphy combined with an analysis of vibrocore samples most of the long term morphological changes in the longe de boyard can be explained by the short term dynamics involving sand transport convergence driven by both tides and waves seaward the changes in the axial part of the bank correspond mainly to erosion and can be explained by wave and tide ravinment shoreward sediment accretion is related to the convergence of tide related sand transport during ebb and flood due to the dam effect of the crest of the bank the changes in the sandbank since 1824 can also be related to a decrease in the tidal channel cross section the latter was the result of a 10 decrease in tidal currents and tidal prisms subsequent to the rapid sediment infill and a related 20 reduction in the water volume of the estuary system where the sandbank lies seismic stratigraphy and cores showed that the modern sandbank consists of upper clinoforms made of fine sand built up over a core made of coarse sand and gravel related to high energy environments hence the longe de boyard is not only the result of sand convergence driven by both tides and waves but also integrates decreases in the tidal prism subsequent to sediment infilling of the surrounding estuaries on a century and millenia time scale