ArticlePDF Available

Buried fluvial incisions as a record of Mid-Miocene sea-level fall on the (northern Bay of Biscay) South Armorican Plateau.

Authors:
A preview of the PDF is not available
... The Southern Brittany shelf is located on the passive margin of the north-eastern Atlantic, and is formed by the opening of the Bay of Biscay by rifting at the end of the Early Cretaceous (Aptian/Albian) (Montadert, 1979). The Late Cretaceous and Late Miocene (Guillocheau et al., 2003;Paquet et al., 2010) sedimentary cover sequence is carbonate dominated with episodic deposition of terrigenous strata . High amplitude oscillations of the mean-sea level during the Quaternary, associated with strong climatic variability, are usually considered as the main causes of shallow incision of river valleys (Figure 2) at the top of these Neogene deposits (Menier et al., 2006). ...
... On the Southern Brittany inner shelf (0 to −50 m water depth), the ages of the incisions and infillings are still debated because of the paucity of radiocarbon dateable material. In the Bay of Étel/Bay of Lorient ( Figure 2B), the timing of incision is speculative and could roughly correspond to a diachronous surface shaped during the sustained periods of lowered sea level between the middle and late Pleistocene (Chaumillon et al., 2008;Estournès et al., 2012;Menier et al., 2006, Paquet et al., 2010 The sedimentary infill is attributed to the last post-glacial transgression and is composed of tidal muddy sand deposits passing upwards to marine coarse sand sheets (Chaumillon et al., 2008;Menier et al., 2006;Sorrel et al., 2010). However, a basal unit interpreted as braided river deposit has been identified on the (Menier et al., 2006;Proust et al., 2001). ...
Article
Full-text available
Menier, D.; Mathew, M.; Cherfils J.-B.; Ramkumar, M.; Estournès, G.; Koch, M.; Guillocheau F.; Sedrati, M.; Goubert, E.; Gensac, E.; Le-Gall, R., and Novico, F., 2019. Holocene sediment mobilization in the inner continental shelf of the Bay of Biscay: Implications for regional sediment budget offshore to onshore. Sediment mobilization, especially from offshore bay to the coast during the Holocene, along the inner continental shelf of Bay of Biscay is less understood. Acoustic and sediment sampling and surveys were conducted offshore of the Bay of Étel to define the shallow geologic framework and the sedimentology. Results of these campaigns are used to identify and map Holocene deposits, discuss sediment transport pathways and depth of closure using Hallermeier's approach in order to define the active sedimentary prism using the depth of closure on a meso-tidal and wave dominated coast. In the Bay of Étel, Holocene sediments are concentrated between rocky shoals and emerged rocks, passing from external zone by sand lobe, 20 m thick to the medium zone, 15 m thick, to the beaches of the Gâvres-Penthièvre beach dune system (modern coastal prism). This case study found that the thickest deposits of Quaternary sediments observed along the inner shelf have a strong dependence on coastal topography and structural heritage. The presence of offshore basement shoal has been determined to have exercised control over sediment transfers from offshore to landward regions during the last marine inundation. Due to the lack of any significant modern fluvial input of sand in the region, the Holocene deposits are inferred to have been derived by reworking of relict Pleistocene and older inner-shelf deposits. Sediment textural trends and seafloor morphology from the medium zone to the beach dune system indicate an absence of relationships (linking) between the modern sedimentary prism and the potential source of sediment to the shoreline. ADDITIONAL INDEX WORDS: Depth of closure, coastline variations, sediment transport, geomorphological behavior, spatio-temporal scale, Hallermeier.
... Morphology of the incised valleys and stratigraphy of their sedimentary filling have been described previously (Proust et al. 2001, Paquet et al. 2010, Chaumillon et al. 2010, Estournes et al. 2012, Traini et al. 2013. The valleys are oriented at right angles or appear parallel to the south Brittany coast, and range in width from 200 m to 4000 m ( Fig. 2; Table 1). ...
... Reflectors with a regional extent (Proust et al. 2001, Paquet et al. 2010, Chaumillon et al. 2010, Estournes et al. 2012, Traini et al. 2013 were georeferenced on each profile by digital seismic picking on Kogeo Seismic Toolkit before time-to-depth conversion. Each picking on every profile was then spatially localized in x, y (geographic coordinates) and in z (in two way travel time in ms) allowing to produce the regional topographic reconstitution of each picked reflector by interpolation, with a resolution of 500 m in latitude and 300 m in longitude. ...
Article
Full-text available
From the Glénan Island to Guérande plateau in south Brittany (France, Bay of Biscay), based on 10000 km of seismic lines, submerged rocky barriers/inherited structural elements were interpreted as the primary controls on variance of coastal topography and incision of palaeovalleys. Sediment infilling is regulated by valley morphology and fluctuation of energy conditions since the last marine transgression associated with the opening of the sea which in turn is a function of climate warming and sea level rising. Dynamics of sedimentation and their subsequent preservation are governed by the shape of the valley and exposure to coastal weather action. Given these structural, geomorphic and climatic constraints, the shoreward transport of sandy sediments is impeded. Thus, coastal topography and structural inheritance are critical factors determining volume of sediments transferred between seaward and landward regions.
... Numerous articles have been published worldwide over the past 20 years concerning the stratigraphic geology and infilling of incised valleys (Allen & Posamentier, 1993;Dalrymple et al., 1992;Zaitlin et al., 1994). On the Atlantic seaboard, several studies, conducted in the 1990s and during the first decade of this century, have clarified the infilling patterns of the "fossil" valleys leading out onto the continental plateau (Proust et al., 2001;Lericolais et al., 2001;Fénies & Lericolais, 2005;Menier et al., 2006;Chaumillon et al., 2006;Thinon et al., 2009, Paquet et al., 2010. Since then, new very-high-resolution seismic data have been acquired in more sheltered environments, less exposed to the action of physical elements such as waves and wind. ...
Article
Full-text available
The late Quaternary sedimentary architecture of the Golfe de Morbihan, a bedrock-controlled lagoonal basin with low sediment supply, was studied by applying an approach based on high-resolution seismic stratigraphy. The present-day environment is characterized by a wave-dominated regime and also shows some local tidal influence. Indeed, the Gulf of Morbihan is connected to the Bay of Quiberon by a narrow tidal pass (rocky sill) where the surface tidal currents reach velocities of up to 2.2 m/s during the flood and 1.8 m/s during the ebb. Wave influence is reduced and confined in the eastern part (inner zone) of the gulf. Flood and ebb tidal currents constrained by basement highs cause a separation between gravel, sand and mud particles. The channel-fill architecture is strongly dependent on tidal current velocity and the geomorphological setting. In the western part of the gulf (outer zone), near the tidal pass, erosion and sediment transport processes are enhanced along the axis of the tidal channel, because of the increased velocity of tidal currents. The outer tidal channel is scoured and the strong currents transport sand (lithic and biolithic fragments) and gravels, which are later deposited along the channel margins. In the central part of the gulf, the hydrodynamic conditions are of slightly weaker energy, and infilling takes places along the axes of the tidal channel, with sedimentation being dominated by a moderate to low-energy regime with fine sands and muds. The channel-fill architecture is composed of lateral-accretion bedding and small elongate tidal bars. In the eastern part of the gulf, tidal currents are very weak, and tidal channels are mainly filled with muddy facies, containing fluid muds in the channel bottom.
Article
Full-text available
Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 105to 107 years, rhythmic or periodic cycles driven by orbital processes with 104- to 106-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 103 to 105 years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.
Article
This paper has 2 objectives: 1st to assist in the dating and palaeoenvironmental interpretation of the Neogene succession of the SW Approaches (S Celtic Sea), 2nd in so doing, to assess the potential use of Neogene dinoflagellate cyst biostratigraphy in this area. The palaeoenvironment throughout the succession is deduced to have been inner to outer neritic, although quite distant from the shoreline, and appears not to have varied very much. Dinoflagellate cyst biostratigraphy has clear potential in helping to resolve stratigraphic problems in the Neogene succession of the SW Approaches.-from Author