Colmatage sédimentaire des marais maritimes et variations relatives du niveau marin au cours des 6 000 dernières années en rade de Brest (Finistère)

Stéphan, Pierre

doi:10.4000/norois.3659

Cited by 19 publications

(35 citation statements)

References 53 publications

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“…The Beg-an-Dorchenn and St Urnel sites, located on highs, were occupied (Giot, 1974). At other places in Brittany, between 2800 and 2500 BP, Morzadec-Kerfourn (1974) and Stephan (2011aStephan ( , 2011b) observed a potential 'regression' of −4 and −2 m, respectively, in non-tuned RSL. Again, this 'regression' may be interpreted in terms of a storm abrasion platform favouring regressive incision in unconsolidated sediments, and thus an artificial lowering of the RSL record (Goslin, 2014;Goslin et al, 2013).…”

Section: Onset Of the Recent Dune Field (2850-450 Bp): The 'Old' Dunesmentioning

confidence: 98%

Middle- to late-Holocene storminess in Brittany (NW France): Part I – morphological impact and stratigraphical record

Vliët-Lanoé¹,

Goslin²,

Hallégouët³

et al. 2014

The Holocene

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Our study aims to understand the recurring climatic conditions prevailing during the largest storms reaching NW France (Brittany). These storms are responsible for the breaching of coastal barriers and major flooding of lowlands. In a first part of our work, we examine the morphological impact and stratigraphic record of storm events along Western Brittany rocky coasts, with a special focus on the southern coast of the Bay of Audierne, the most exposed coast of the region. In a second paper ('Middle-to Late-Holocene Storminess in Brittany (NW France): Part II'), we shall focus on the chronology of storm events and their climate forcing conditions. Drilling transects and stratigraphic analyses were first undertaken to constrain chronology, strength and wind direction during the main Holocene storm events. New dates, observations and a relative sea-level (RSL) curve were then used to inform discussion of the necessary climatic and morphologic conditions leading to destructive storm events. Most recorded events appear to be linked with cooling episodes of the Holocene and a RSL close to present. Some storms are clearly responsible for breaching and dune building or remobilisation. We demonstrate that storm frequency and intensity appear to rise in a stepwise manner during the late Holocene. Maximum efficiency is reached during the 'Little Ice Age' with clustered events probably lasting several days, but major storms also occurred immediately prior to the 'Medieval Warm Period'. We suggest that recent coastal dune building from c. ad 1100 until now, despite a sea level close to present and continuously rising, may be a direct consequence of the restoration of beaches after periods of recurrent storminess. This building activity often occurred during dry negative North Atlantic Oscillation (NAO) events, in connection with the available sedimentary supply.

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Section: Onset Of the Recent Dune Field (2850-450 Bp): The 'Old' Dunesmentioning

confidence: 98%

Middle- to late-Holocene storminess in Brittany (NW France): Part I – morphological impact and stratigraphical record

Vliët-Lanoé¹,

Goslin²,

Hallégouët³

et al. 2014

The Holocene

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“…The other four layers are characterized by their content of abundant juveniles and adults gastropod shells of Turritella communis; all are extremely well preserved, which is not in agreement with a high-energy event such as a storm. We name them T1 at 0.90 m Cassen et al, 2011;Guilcher and Allegouet, 1991;Morzadec-Kerfourn, 1974Stephan, 2011;Ters, 1973), chronozones (Morzadec-Kerfourn, 1974) and Flandrian transgressive fluctuations (Jelgersma et al, 1979;L'Homer et al, 2006). This diagram shows the coincidence of the climatic events recorded in core MD08-3204CQ, from S1 to S6 (storms events) and T1 to T4 (the Turritellid layers) indicated by dashed lines, with periods of rapid climatic change described in the literature (Bond et al, 2001;Mayewski et al, 2004).…”

Section: The Upper Interval From 380 To 120 M: Sedimentary Unit U3mentioning

confidence: 99%

Climatically-driven impacts on sedimentation processes in the Bay of Quiberon (south Brittany, France) over the last 10,000 years

et al. 2014

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The Bay of Quiberon (NW France), which is protected by the Quiberon Peninsula, provides well-preserved sedimentary archives for high-resolution reconstruction of Holocene climate variability. Very-high-resolution seismic profiles were obtained from two Seistec boomer seismic campaigns conducted in the bay. The seismic surveys reveal the deposition of five distinct sedimentary units. This succession is correlated with radiocarbon-dated sediments sampled in a long CASQ core (MD08-3204CQ). The analysis of the sediments shows significant changes in grain size, indicating a complex series of palaeo-climate events dated at 8800, 8600, 4270, 3860, 2470 and 1060 cal. yr BP. These may be correlated with millennial timescale climate variability corresponding to the phases of Holocene rapid climate changes (RCCs), associated with negative North Atlantic Oscillation (NAO) index and usually characterized by weaker winter storms. On the contrary, periods between RCCs are characterized by the predominance of westerly winds and stormy conditions for Brittany (i.e. positive NAO). However, only storm events occurring during the RCCs have been preserved in the Bay of Quiberon. This paper aims to reconstruct the Holocene sedimentary infill of the bay, highlighting the role of episodic acceleration phases of the sea-level rise on the preservation of sedimentary archives. Thus, the Bay of Quiberon provides substantially a complete sedimentation record of the last 10,000 years characterized by a series of complex palaeo-environmental changes.

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“…This rise of sea-level is not sufficient to enable a widespread of large amout of sediments. Field observations indicate that the base of unconsolided cliffs is nowdays rarely reached by waves attack (Stéphan 2011a). Furthermore, the presence of a large platform in front of the current cliffs promotes the dissipation of wave energy before it reaches the foot of the cliff.…”

Section: The Question Of Sediment Supply From Periglacial Cliff Erosimentioning

confidence: 99%

“…The spit of Linkin is also sheltered from dominant waves by a rocky promontory. Finally, the Bay of Brest is a fetch-limited environment and the waves height never exceed 1 m, whatever the wind conditions (Stéphan, 2011a). According to their general orientation to incident waves, spits are swash-or drift-aligned ( fig.…”

Section: General Settingmentioning

confidence: 99%

“…Benthic foraminifera assemblages were analysed to identify the exposure of the salt-marshes and to determine the phases of construction and breakdown of gravel spits. The characterization and the chronology of environmental conditions associated to sedimentary units were improved by using a foraminifera-based transfer function and twenty radiocarbon dates (Stéphan 2011a).…”

Section: Long-term (10 3 Yr) Evolution Of Gravel Spits Of Brittanymentioning

confidence: 99%

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Long-, Mid- and Short-Term Evolution of Coastal Gravel Spits of Brittany, France

Stéphan

Suanez

Fichaut

2015

Sand and Gravel Spits

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International audienceGravel spits of Brittany have experimented a long morphosedimentary evolution over the last millenia. Based on analysis of several back-barrier holocene sediment stratigraphies, distinct phases of construction and barrier breakdown were recognized, indicating the role played by storminess and sediment supply during the late-holocene period. Over the last centuries and decades, a deficit of sediment bubget affecting several gravel spits is highlighted. Therefore, actual coastal evolution of most of them is mainly dominated by cannibalization, landward retreat by rollover and complete destruction of the spits in some places. This coastal erosion is related to the lack of significant offshore sediment input or from the erosion of unconsolided cliffs. Locally, anthropogenic forcing have axacerbated the erosion processes by sediment minings and/or the construction of hard defense structures. For the swash-aligned gravel spits, frequency and magnitude of overwash processes is controlling the rate of landward retreat by rollover. This morphodynamic behaviour is illustrated by topo-morphological surveys realised between 2002 and 2012 on Sillon de Talbert spit which has experienced a complete crestal removal during the 10 March 2008 Johanna storm. Although this event have a 50-100yrs occurence, the barrier has exhibited a rapid crestal rebuilding by overtopping processes, illustrating the great resilience of the spit. Thus, coastal erosion management strategies mainly based on hard defense structures are gradually abandoned for new management policies based on soft operations. Nowadays, gravel spits of Brittany are also considered as a geological heritage and management plans are establishing by local authorities. 1. GENERAL SETTING In Brittany, gravel beaches are located mainly on the northern and western coast (fig. 1). Their construction is mainly due to the shoreward removing of periglacial deposits initially accumulated on the coastal shelf during the post-glacial marine transgression. The southern part of Brittany is characterized by sandy beaches and coastal dunes, except locally where a coarse material is provided by erosion of cliffs formed by Pleistocene deposits (head). Nowadays, unconsolidated cliffs are considered as the most significant source of coarse sediments in Brittany (Guilcher et al. 1957, 1990). In the Bay of Brest, the highly weathered of shale cliffs also contribute locally to feed the gravel barriers. In the Bay of Brest, the indentations of the jagged coastline were favorable to the construction of a numerous smale-scale barriers and spits with a high morphological diversity (fig. 2A to 2D). The lenght and the volume of gravel spits in the bay of Brest never exceed 700 m and 100.000 m 3 respectively. Nevertheless, the Sillon de Talbert spit studied in the north of Brittany forms the bigger accumulation reaching 3.2 km long and sediment volume estimated at 1.23 x 10 6

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Colmatage sédimentaire des marais maritimes et variations relatives du niveau marin au cours des 6 000 dernières années en rade de Brest (Finistère)

Cited by 19 publications

References 53 publications

Middle- to late-Holocene storminess in Brittany (NW France): Part I – morphological impact and stratigraphical record

Middle- to late-Holocene storminess in Brittany (NW France): Part I – morphological impact and stratigraphical record

Climatically-driven impacts on sedimentation processes in the Bay of Quiberon (south Brittany, France) over the last 10,000 years

Long-, Mid- and Short-Term Evolution of Coastal Gravel Spits of Brittany, France

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