How do river channels aggrade? An investigation into the importance of upstream drivers (water discharge and sediment supply) on sediment aggradation using analogue modelling

2020 ◽  
Author(s):  
Stephen E. Watkins ◽  
Nikhil Sharma ◽  
Luis Valero ◽  
Maxime Tremblin ◽  
Abdallah S. Zaki ◽  
...  
Keyword(s):  
Sea Level ◽  
Environmental Changes ◽  
Water Discharge ◽  
Scale Up ◽  
Sediment Supply ◽  
River Channels ◽  
Fluvial System ◽  
Fluvial Deposits ◽  
Analogue Modelling ◽  
Stratigraphic Architecture

<p><span>Stratigraphic architecture of fluvial deposits is often interpreted as a record of changes in accommodation created by absolute sea-level change, subsidence, or a combination of both (downstream drivers). An increase or decrease in accommodation causes the fluvial system to respond by either aggrading or degrading to a new equilibrium slope. However, in recent years the role of upstream drivers, such as water discharge and sediment supply (volume and grain-size distribution), in controlling equilibrium slopes has gained more importance, however we still lack significant understanding of these upstream processes. It is important to be able to differentiate between stratigraphy influenced by upstream and downstream drivers in the field because fluvial deposits represent an important archive of environmental changes.  Traditionally, downstream drivers are often invoked to explain past accommodation changes, but in actuality there are rarely robust constraints on the cause of these space changes. At present there is still no well-documented examples of upstream versus downstream driven stratigraphic architecture. One way to address this issue is by undertaking analogue modelling (i.e. flume experiments) as this permits the isolation of individual parameters, such as water discharge, and allows us to investigate their role on the fluvial system in a controlled environment. </span></p><p><span> </span></p><p><span>In the first part of the project that we present here, we investigate how sediment aggradation within a channel develops through time by using a quasi-2D flume.  We have designed and manufactured a narrow (0.05 m), long (2.4 m) flume with an initial gradient of zero.  We aim to (i) investigate how aggradation occurs through time using a series of different water discharges, sediment supplies and sediment concentrations and observe the resulting equilibrium slopes; (ii) perturb the system once equilibrium is reached to observe the readjustment of the system to new conditions; (iii) carry out a series of experiments varying downstream drivers (i.e. sea-level) which theoretically produce the same amount of aggradation as the upstream parameters we have used do, we will then be able to compare any similarities or differences in stratigraphy.  Ultimately we will use these results to scale up to a fully three-dimensional analogue model (i.e. a wide flume, approximately 1 m) that produces channels and floodplains.  We can then investigate how the upstream and downstream changes seen in the narrow flume are translated into the wider flume.</span></p>

scholarly journals Holocene sea level and climate interactions on wet dune slack evolution in SW Portugal: A model for future scenarios?

The Holocene ◽  
2018 ◽  
Vol 29 (1) ◽  
pp. 26-44 ◽  
Author(s):  
Manel Leira ◽  
Maria C Freitas ◽  
Tania Ferreira ◽  
Anabela Cruces ◽  
Simon Connor ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Environmental Changes ◽  
Sediment Accumulation ◽  
High Energy ◽  
Sediment Supply ◽  
Dune Slack ◽  
Ecological Stability ◽  
The Holocene ◽  
Climate Interactions

We examine the Holocene environmental changes in a wet dune slack of the Portuguese coast, Poço do Barbarroxa de Baixo. Lithology, organic matter, biological proxies and high-resolution chronology provide estimations of sediment accumulation rates and changes in environmental conditions in relation to sea-level change and climate variability during the Holocene. Results show that the wet dune slack was formed 7.5 cal. ka BP, contemporaneous with the last stages of the rapid sea-level rise. This depositional environment formed under frequent freshwater flooding and water ponding that allowed the development and post-mortem accumulation of abundant plant remains. The wetland evolved into mostly palustrine conditions over the next 2000 years, until a phase of stabilization in relative sea-level rise, when sedimentation rates slowed down to 0.04 mm yr−1, between 5.3 and 2.5 cal. ka BP. Later, about 0.8 cal. ka BP, high-energy events, likely due to enhanced storminess and more frequent onshore winds, caused the collapse of the foredune above the wetlands’ seaward margin. The delicate balance between hydrology (controlled by sea-level rise and climate change), sediment supply and storminess modulates the habitat’s resilience and ecological stability. This underpins the relevance of integrating past records in coastal wet dune slacks management in a scenario of constant adaptation processes.

scholarly journals Deciphering tectonic, eustatic and surface controls on the 20 Ma-old Burdigalian transgression recorded in the Upper Marine Molasse in Switzerland

2019 ◽  
Author(s):  
Philippos Garefalakis ◽  
Fritz Schlunegger
Keyword(s):  
Sea Level ◽  
Depositional Environments ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Crustal Material ◽  
Molasse Basin ◽  
Shallow Marine ◽  
Depositional Settings ◽  
Stratigraphic Architecture ◽  
Aar Massif

Abstract. The stratigraphic architecture of the Swiss Molasse basin reveals crucial information about the basin’s geometry, its evolution and the processes leading to the deposition of the clastic material. Nevertheless, the formation of the Upper Marine Molasse (OMM) and the controls on the related Burdigalian transgression are not fully understood yet. During these times, from c. 20 to 17 Ma, the Swiss Molasse basin was partly flooded by a peripheral shallow marine sea, striking SW – NE. We proceeded through detailed sedimentological and stratigraphic examinations of several sites across the entire Swiss Molasse basin in order to deconvolve the stratigraphic signals related surface and tectonic controls. Surface-related signals include stratigraphic responses to changes in eustatic sea level and sediment fluxes, while the focus on crustal-scale processes lies on the uplift of the Aar-massif at c. 20 Ma. Field examinations show, that the evolution of the Burdigalian seaway was characterized by (i) shifts in the depositional settings, (ii) changes in discharge directions, a deepening and widening of the basin, and (iv) phases of erosion and non-deposition. We relate these changes in the stratigraphic records to a combination of surface and tectonic controls at various scales. In particular, roll-back subduction of the European mantle lithosphere, delamination of crustal material and the associated rise of the Aar-massif most likely explain the widening of the basin particular at distal sites. In addition, the uplift of the Aar-massif was likely to have shifted the patterns of surface loads. These mechanisms could have caused a flexural adjustment of the foreland plate underneath the Molasse basin, which we use as mechanism to explain the establishment of distinct depositional environments and particularly the formation of subtidal-shoals where a lateral bulge is expected. In the Alpine hinterland, these processes occurred simultaneously with a period of fast tectonic exhumation accomplished through slip along the Simplon detachment fault, with the consequence that sediment flux to the basin decreased. It is possible that this reduction in sediment supply contributed to the establishment of marine conditions in the Swiss Molasse basin and thus amplified the effect related to the tectonically controlled widening of the basin. Because of the formation of shallow marine conditions, subtle changes in the eustatic sea level contributed to the occurrence several hiatus that chronicle periods of erosion and non-sedimentation. While these mechanisms are capable of explaining the establishment of the Burdigalian seaway and the formation of distinct sedimentological niches in the Swiss Molasse basin, the drainage reversal during OMM-times possibly requires a change in the tectonic processes at the slab scale. We conclude that sedimentological records can be used to decipher surface controls and lithospheric-scale processes in orogens from the stratigraphic record, provided that a detailed sedimentological and chronological database is available.

scholarly journals Interactions between channels and tributary alluvial fans: channel adjustments and sediment-signal propagation

2019 ◽  
Author(s):  
Sara Savi ◽  
Stefanie Tofelde ◽  
Andrew D. Wickert ◽  
Aaron Bufe ◽  
Taylor F. Schildgen ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Signal Propagation ◽  
Main Channel ◽  
Alluvial Fan ◽  
Sediment Supply ◽  
Alluvial Fans ◽  
Fluvial System ◽  
Channel Network ◽  
Fluvial Deposits ◽  
The Impact

Abstract. Climate and tectonics impact water and sediment fluxes to fluvial systems. These boundary conditions set river form and can be recorded by fluvial deposits. Reconstructions of boundary conditions from these deposits, however, is complicated by complex channel-network interactions and associated sediment storage and release through the fluvial system. To address this challenge, we used a physical experiment to study the interplay between a main channel and a tributary under different forcing conditions. In particular, we investigated the impact of a single tributary junction, where sediment supply from the tributary can produce an alluvial fan, on channel geometries and associated sediment-transfer dynamics. We found that the presence of an alluvial fan may promote or prevent sediment to be moved within the fluvial system, creating different coupling conditions. A prograding alluvial fan, for example, has the potential to disrupt the sedimentary signal propagating downstream through the confluence zone. By analyzing different environmental scenarios, our results indicate the contribution of the two sub-systems to fluvial deposits, both upstream and downstream of the tributary junction, which may be diagnostic of a perturbation affecting the tributary or the main channel only. We summarize all findings in a new conceptual framework that illustrates the possible interactions between tributary alluvial fans and a main channel under different environmental conditions. This framework provides a better understanding of the composition and architecture of fluvial sedimentary deposits found at confluence zones, which is essential for a correct reconstruction of the climatic or tectonic history of a basin.

scholarly journals Lower Badenian coarse-grained Gilbert deltas in the southern margin of the Western Carpathian Foredeep basin

2018 ◽  
Vol 69 (1) ◽  
pp. 89-113 ◽  
Author(s):  
Slavomír Nehyba
Keyword(s):  
Sea Level ◽  
Foreland Basin ◽  
Sediment Supply ◽  
Coarse Grained ◽  
Basal Surface ◽  
Relative Sea Level ◽  
Sediment Delivery ◽  
Southern Margin ◽  
Stratigraphic Architecture ◽  
Carpathian Foredeep

AbstractTwo coarse-grained Gilbert-type deltas in the Lower Badenian deposits along the southern margin of the Western Carpathian Foredeep (peripheral foreland basin) were newly interpreted. Facies characterizing a range of depositional processes are assigned to four facies associations — topset, foreset, bottomset and offshore marine pelagic deposits. The evidence of Gilbert deltas within open marine deposits reflects the formation of a basin with relatively steep margins connected with a relative sea level fall, erosion and incision. Formation, progradation and aggradation of the thick coarse-grained Gilbert delta piles generally indicate a dramatic increase of sediment supply from the hinterland, followed by both relatively continuous sediment delivery and an increase in accommodation space. Deltaic deposition is terminated by relatively rapid and extended drowning and is explained as a transgressive event. The lower Gilbert delta was significantly larger, more areally extended and reveals a more complicated stratigraphic architecture than the upper one. Its basal surface represents a sequence boundary and occurs around the Karpatian/Badenian stratigraphic limit. Two coeval deltaic branches were recognized in the lower delta with partly different stratigraphic arrangements. This different stratigraphic architecture is mostly explained by variations in the sediment delivery and /or predisposed paleotopography and paleobathymetry of the basin floor. The upper delta was recognized only in a restricted area. Its basal surface represents a sequence boundary probably reflecting a higher order cycle of a relative sea level rise and fall within the Lower Badenian. Evidence of two laterally and stratigraphically separated coarse-grained Gilbert deltas indicates two regional/basin wide transgressive/regressive cycles, but not necessarily of the same order. Provenance analysis reveals similar sources of both deltas. Several partial source areas were identified (Mesozoic carbonates of the Northern Calcareous Alps and the Western Carpathians, crystalline rocks of the eastern margin of the Bohemian Massif, older sedimentary infill of the Carpathian Foredeep and/or the North Alpine Foreland Basin, sedimentary rocks of the Western Carpathian/Alpine Flysch Zone).

Paleohydraulic investigation of the Ebro Basin: Implications for Mars

2021 ◽  
Author(s):  
Heath Geil-Haggerty
Keyword(s):  
Water Discharge ◽  
Sedimentary Basins ◽  
Mass Conservation ◽  
Sediment Supply ◽  
Sediment Flux ◽  
River Channels ◽  
Ebro Basin ◽  
Fluvial Systems ◽  
Sediment Size ◽  
Basin Scale

<p>The stratigraphy preserved in Earth’s sedimentary basins offers a record of how landscapes have evolved with time.  This stratigraphy provides insights into the dynamic processes that shaped the surface of the earth.  Fluvial stratigraphy contains many elements that can be used to recreate past conditions in ancient river channels.  Paleohydraulic reconstruction uses measurements of fluvial stratigraphy to model the conditions in the system that created them.  This allows us to answer questions related to water discharge, sediment flux, and duration of fluvial activity.  These are key questions when investigated in the context of Mars.  Paleohydraulic models can be used as compelling analogs for similar systems on Earth as well as Mars and other rocky planets.           </p><p>This study examines what the record of Oligocene-Miocene fluvial stratigraphy in northeastern Spain’s Ebro Basin can tell us about water discharge and sediment flux across distributive fluvial systems at a basin scale.  The Cenozoic stratigraphy of northeastern Spain’s triangular shaped Ebro Basin embodies a classic example of the formation of a closed sedimentary basin.  The Ebro Basin contains a number of remarkably well exposed fluvial sedimentary deposits.  These deposits outcrop as distinctive laterally contiguous channel sand bodies.  Clastic sediment supply in the Ebro Basin is largely governed by tectonic uplift and basin subsidence related to the Pyrenean orogen with peripheral contributions from the Catalan Coast and Iberian Ranges.  We test the idea that the record of conditions in the fluvial systems should reflect the record of lacustrine chemical sediments through sediment mass conservation.  In order to test this hypothesis measurements of bedform height, barform height, sediment size, and paleochannel dimensions were collected in the field.  Our paleohydraulic model uses previously derived theoretical and empirical relationships to recreate the conditions in these ancient fluvial systems.  These results are scaled up by accounting for drainage density and intermittency in order to address the principal question at a basin scale.  Paleodischarges from the fluvial sediments are comparable to those from river chemistry calculations for the lacustrine facies. </p>

Integrating biogeomorphic feedbacks in the coastal zone to bolster coastal resiliency

2021 ◽  
Author(s):  
Cindy Palinkas ◽  
Lorie Staver
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Management Strategy ◽  
Environmental Changes ◽  
Sediment Supply ◽  
Coastal Protection ◽  
Coastal System ◽  
Living Shorelines ◽  
Accretion Rates ◽  
Created Marshes

<p>Living shorelines, defined in this study as narrow marsh fringes with adjacent sills, have been gaining traction as the preferred management strategy to mitigate shoreline erosion. These nature-based features provide the same ecosystem services as natural marshes while protecting coastlines. However, they also are threatened by the same environmental changes (sea-level rise, changing sediment supply) as natural marshes and may change characteristics of adjacent subtidal sediments. This study evaluates the role of plants in both the created marshes of living shorelines and, where present, beds of submersed aquatic vegetation (SAV) in the adjacent subtidal in the effectiveness, impacts, and resiliency of living shorelines over ~10 years in mesohaline Chesapeake Bay. At study sites, there is a net seaward movement of shorelines with living shoreline installation due to construction technique. This movement replaces shallow-water habitat immediately adjacent to the pre-existing shoreline; farther offshore, sedimentological changes vary among sites but do not appear to drive changes in the presence/absence of subtidal SAV. While current accretion rates in the created marshes are greater than local relative sea-level rise, there is evidence that accretion rates increase with marsh age, suggesting that living shorelines are most vulnerable in the first few years after installation. Because nutrient burial is maximized when SAV occur next to living shorelines, a management strategy that considers the subtidal and intertidal as integrated components of the coastal system is needed to optimize co-benefits of coastal protection.</p>

Understanding fluvial aggradation styles through physical modelling: Are we able to distinguish changes in water discharge and/or sediment supply (upstream drivers) from changes in base-level (downstream forcing) on river aggradation?  

2021 ◽  
Author(s):  
Stephen E. Watkins ◽  
Guy Simpson ◽  
Laure Guerit ◽  
Frédéric Arlaud ◽  
Valentin Marguin ◽  
...  
Keyword(s):  
Sea Level ◽  
Water Discharge ◽  
Physical Modelling ◽  
Bedload Transport ◽  
Sediment Supply ◽  
Low Flow ◽  
Small Scale ◽  
Base Level ◽  
River Bed ◽  
Bed Evolution

<p>Fluvial stratigraphy is the product of changes in Earth’s history and inverting this record has often resulted in interpretations associated with changes in base-level caused by sea-level and/or basement subsidence (downstream drivers).  Similarly, environmental perturbations occurring in the upstream reaches of a fluvial system (i.e., the source region), such as climate driven changes of water discharge and/or perturbations of sediment supplied to rivers (upstream drivers), can also drive river bed evolution.  Therefore, both changes in upstream and downstream drivers can cause a river’s equilibrium profile to respond and adjust through aggradation or degradation and hence generate stratigraphy.  Furthermore, it is likely to have changes in both upstream and downstream drivers simultaneously because both drivers may be themselves driven by the same factors e.g., astronomical cycles can drive both sea-level variation at the downstream end of fluvial systems and water discharge variations in the upstream end.  Deciphering the effects of the two drivers is vital to be able to comprehensively interpret the narrative of Earth’s history preserved in fluvial successions.  We explore this issue with river flume experiments, where we are able to test the influence of both upstream and downstream drivers in isolation.  Furthermore, the small scale of physical modelling reduces the spatial and temporal timescales compared to natural systems and allows us to investigate how quickly the system responds.</p><p>We use a narrow (0.05 m), long (2.25 m) flume with an initial gradient of zero.  Side-profile photos are taken throughout the experiment run, which are then analysed and fitted to monitor river bed evolution.  Top view photos record channel dimensions.  We use low flow rates (~<600 ml/min) delivered by a peristaltic pump, to avoid turbulence and ensure bedload transport.  We have three aims with our experiments. Firstly, to investigate the role of changes in water discharge and sediment supply on equilibrium river profiles and the timescales associated.  Secondly, to carry out a series of perturbation experiments varying downstream drivers (i.e., sea-level), which theoretically produce the same amount of aggradation as the upstream parameters we have used in order to compare.  Thirdly to vary both upstream and downstream parameters simultaneously to investigate the effects. Results to date suggest that the growing wedge maintains a relatively constant slope and that the slope of the wedge is dependent on sediment concentration (sediment discharge/water discharge), when using the same grain-size distribution for each experiment.  Furthermore, results imply that the system is highly sensitive to perturbations when the setup of the system is with relatively low sediment concentrations. Therefore, a greater magnitude of response is seen than with setups of higher sediment concentrations. Currently we are undergoing perturbation experiments and downstream perturbations, the results of which will also be presented here. Ultimately we will use our findings to upscale our experiments into a fully 3-D flume tank that will grow as an unconfined fan in order to observe any similarities and differences.</p>

scholarly journals Interactions between main channels and tributary alluvial fans: channel adjustments and sediment-signal propagation

2020 ◽  
Vol 8 (2) ◽  
pp. 303-322
Author(s):  
Sara Savi ◽  
Stefanie Tofelde ◽  
Andrew D. Wickert ◽  
Aaron Bufe ◽  
Taylor F. Schildgen ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Signal Propagation ◽  
Main Channel ◽  
Alluvial Fan ◽  
Sediment Supply ◽  
Alluvial Fans ◽  
Fluvial System ◽  
Channel Network ◽  
Fluvial Deposits ◽  
The Impact

Abstract. Climate and tectonics impact water and sediment fluxes to fluvial systems. These boundary conditions set river form and can be recorded by fluvial deposits. Reconstructions of boundary conditions from these deposits, however, is complicated by complex channel–network interactions and associated sediment storage and release through the fluvial system. To address this challenge, we used a physical experiment to study the interplay between a main channel and a tributary under different forcing conditions. In particular, we investigated the impact of a single tributary junction, where sediment supply from the tributary can produce an alluvial fan, on channel geometries and associated sediment-transfer dynamics. We found that the presence of an alluvial fan may either promote or prevent the movement of sediment within the fluvial system, creating different coupling conditions. By analyzing different environmental scenarios, our results reveal the contribution of both the main channel and the tributary to fluvial deposits upstream and downstream from the tributary junction. We summarize all findings in a new conceptual framework that illustrates the possible interactions between tributary alluvial fans and a main channel under different environmental conditions. This framework provides a better understanding of the composition and architecture of fluvial sedimentary deposits found at confluence zones, which can facilitate the reconstruction of the climatic or tectonic history of a basin.

The sea-level signal in Pleistocene shallow-marine records – examples from carbonate and siliciclastic sequences

2020 ◽  
Author(s):  
Barbara Mauz ◽  
Zhixiong Shen ◽  
Natasha Barlow ◽  
David Hodgson ◽  
Colin Woodroffe
Keyword(s):  
Sea Level ◽  
Sea Level Change ◽  
Sediment Supply ◽  
Last Glacial Period ◽  
Shallow Marine ◽  
Level Change ◽  
Isostatic Adjustment ◽  
Accommodation Space ◽  
Stratigraphic Architecture

<p>It is generally accepted that sea-level change represents the most important boundary condition that controls stratigraphic architecture in the shallow-marine area and further downdip. The shallow-marine stratigraphic body is then a result of the changing ratio between sediment supply and accommodation space with a range of local (autogenic) processes interplaying with the eustatic (allogenic) sea level. Extracting the sea-level signal from this interplay is typically approached through rigorous interpretation of the indicative meaning of relevant sea-level markers and through comparison with the most appropriate glacio-isostatic adjustment (GIA) model. The latter comparison is insightful for the last glacial period, but for the Pleistocene it suffers from the dilemma that the GIA contribution to sea-level change cannot be predicted for a specific location unless the ice history is known but this is what the shallow-marine record is trying to reconstruct.</p><p>Here we aim for Pleistocene sea-level reconstructions that are largely independent of GIA predictions. For this we present Pleistocene shallow-marine records from high-, mid- and low-latitudinal settings. The presentation focuses on four aspects: type and quality of the data (e.g. outcrop, borehole, etc), preservation of the record, separation of allogenic versus autogenic signal and completeness of the eustatic cycle.</p><p>We show that in siliciclastic systems the preservation depends on sediment supply and on the coastal energy with which ravinement and regression surfaces obliterate the stratigraphic record. Separating autogenic from allogenic signals depends very much on data quality and the ability to reconstruct the antecedent topography. None of our records show a complete eustatic cycle from lowstand to highstand and back to lowstand where the missing part of the cycle seems to be indicative for the type of shallow-marine record and its location on earth.</p><p>We discuss reasons and implications of our findings and emphasise the need for far greater consideration of stratigraphic architecture, carbonate facies and facies correlation.</p>

scholarly journals Sedimentary record of environmental changes and human interferences in a macrotidal bay for the last millenaries: the Marennes-Oléron Bay (SW France)

2010 ◽  
Vol 181 (2) ◽  
pp. 151-169 ◽  
Author(s):  
Jonathan Allard ◽  
Eric Chaumillon ◽  
Xavier Bertin ◽  
Clément Poirier ◽  
Florian Ganthy
Keyword(s):  
Sea Level ◽  
Environmental Changes ◽  
Land Reclamation ◽  
Morphological Evolution ◽  
Sediment Supply ◽  
Sea Level Changes ◽  
Drainage Pattern ◽  
Sedimentary Record ◽  
Very High ◽  
Sediment Fill

Abstract This synthesis of the morphological and stratigraphical evolutions of the Marennes-Oléron Bay (west coast of France) combines bathymetric data (1824 and 2003) and very high-resolution seismic profiling groundtruthed by vibracore samples. The Marennes-Oléron Bay is characterised by a very high sedimentation rate and appears to be an ideal place to investigate the sedimentary record of the major environmental changes that occurred since the last several millennia. The sediment budget of the Marennes-Oléron Bay, between 1824 and 2003, is clearly positive. The flood-dominated northern Marennes-Oléron Bay displays sediment gain in both intertidal and subtidal areas whereas the ebb-dominated southern Marennes-Oléron Bay displays sediment gain restricted to the intertidal area and deepening of subtidal channels. In addition, human influences such as oyster farming may play a role in the sediment gain of the bay. The sediment-fill of the northern Marennes-Oléron Bay consists of five main phases: (1) lenticular units and flooded intertidal flats recording lower sea level periods before 7500 yr B.P.; (2) tidal channel-fills recording changes in tidal drainage pattern from 7500 to 5000 yr B.P.; (3) a subtidal unit which constitutes the main phase of sediment fill in the northern part of the bay from 5000 to 1500 yr B.P.; (4) a major channelized erosional surface related to huge coastline changes from 1500 to 1000 yr B.P.; and (5) a mud drape emplaced during the last millennia and potentially recording historical human impact (deforestation and land reclamation). The sediment fill of the southern Marennes-Oléron consists of sandbanks, mixed sand-and-mud flats and tidal channels, mainly emplaced under wave-and-tide processes since the last centuries. Despite its relatively thin (20 m at the maximum), recent and rapid sediment fill, the stratigraphic organization and morphological evolution of the Marennes-Oléron Bay is very complex and spatially variable. Like in many other estuaries, sediment fill of the Marennes-Oléron Bay was successively controlled by relative sea level changes, and then by sediment supply driven by hydrodynamic changes related to huge coastline migrations, and finally by human activities. Moreover, this kind of “rocky coast” estuary, where the sediment-fill is very thin and discontinuous, is characterised by a bedrock control at each phases of the sediment fill both in terms of preservation in topographic lows and in terms of control on hydrodynamics and related sediment input.

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