Improvement of grain-size analyses using the automated SEDIGRAPH 5100

The method of analysing fine grained sediments is discussed and an improved technique using a water-glycerol solution of known density instead of water is proposed. Inaccuracies resulting from wet sieving may contribute to explain the observed difference between the pipette method and the Sedigraph 5100 analyses

Применение нейросетевых технологий для измерений параметров вибрации объектов с неплоской поверхностью

Было проведено компьютерное моделирование электродинамической системы интерференционного измерителя параметров вибраций объектов с неплоской поверхностью. Показано, что применение нейросетевых технологий позволяет использовать интерференционный метод для измерения параметров перемещений объектов с неплоской поверхностью. Полученные результаты обработки данных компьютерного моделирования свидетельствуют об эффективности практического применения нейронных сетей для обработки сигналов трёхзондового интерференционного сверхвысокочастотного измерителя.Було проведено комп'ютерне моделювання електродинамічної системи інтерференційного вимірювача параметрів вібрацій об'єктів з неплоскою поверхнею. Показано, що застосування нейромережевих технологій дозволяє використовувати інтерференційний метод для вимірювання параметрів переміщень об'єктів з неплоскою поверхнею. Отримані результати обробки даних комп'ютерного моделювання свідчать про ефективність практичного застосування нейронних мереж для обробки сигналів тризондового інтерференційного надвисокочастотного вимірювача.An electrodynamical system of an interference vibration meter for objects with a non-planar surface is simulated using a computer. It is shown that neural technologies allow to use an interference method for measuring parameters of the moving objects with a non-planar surface. The results obtained of processing data of a computer simulation show the effectiveness of the practical application of neural networks for processing signals of the trisounder interference microwave meter

Évolution historique du prisme littoral du lido de l’étang de Thau (Sète, Sud-Est de la France). Mise en évidence par sismique réflexion très haute résolution = Historical evolution of the littoral prism of the Thau lagoon barrier (Sète, South-East France). Very high-resolution reflection seismic investigation

Very high-resolution seismic data have been obtained recently, in the framework of the research programme PNEC (French National Programme of Coastal Environment), on the shoreline area of Sète (Mediterranean coast, South East France). These data provide an accurate picture of the internal structure of the shoreline body. Seismic results combined with data about the morphosedimentary evolution of the study area, vibrocore data and results from archaeological investigations yield clues to the historical evolution of the study area. Especially, it is pointed out that the functioning of the present-day shoreline, by comparison with the system built in classical times, is characterized by a severe reduction in sediment supply and in volumes of sand involved in the shoreline dynamics

Successions of sea-level changes during the Pleistocene in Mauritania and Senegal distinguished by sedimentary facies study and U/Th dating

International audienc

Processus hydrodynamiques et morphosedimentaires de l'environnement des barres d'avant-cote du littoral du Golfe du Lion

Factors such as the origin of the material involved in the profile equilibrium, or the rate of sea level rise are important in partially controlling the shoreline evolution. In the Gulf of Lions (Mediterranean Sea), the linear and crescentic offshore bars constitute another factor which prevents the use of simple models such as the power function y = ax super(b). A relevant parameter to improve our understanding seems to be the shape of the profile recorded normally to the shore and the definition of its interannual fluctuations. This project works out a number of regular surveys, in time and space, from permanently located landmarks. Each landmark constitutes an observatory and the measurements reported here: bathymetry, topography, sedimentology and coastal oceanography were gathered at the Saint-Cyprien one (Pyrenees-Orientales)

Marine sedimentary environments on some parts of the tropical and equatorial Atlantic margins of Africa during the Late Quaternary

International audienceFrom 18,000 y B.P. up to the Present, major climatic changes combined with eustatic sea-level irregular rise controlled important variations in sedimentary conditions on the Atlantic African margin between 6°S and 21°N. The present shelf deposition of material is also controlled by climatic latitudinal gradients acting on the nature, volume and distribution of terrigenous and carbonate sediments. The evolution of sedimentary conditions during this period may be summarized as follows. Coastal terrigenous deposition Fluvial sands were emplaced in inner shelf paleo-valleys during the beginning of the Wiscon sinian regression, following a major erosion phase providing an important source for the siliciclastic part of the terrigenous influx. In tropical regions (Mauritania, Senegal), aeolian dune sands formed during the arid "glacial" period (the so-called Ogolian) on the emerged shelf, but were destroyed during the subsequent transgression. In the vicinity and south of the Equator (Coˆte d'Ivoire, Congo), aeolian input was reduced but litoral dunes of that period occurred whose remnants may be observed close to the present shoreline. At the lower stand of sea level, fine particles directly by-passed the shelf towards the continental rises and abyssal plains. During the Holocene transgression, the main sedimentary processes occurred only when standstill or slowing of the sea-level rise took place. Then littoral deposits (fine sands of the shore, dune sands and even lagoonal deposits with mangrove peats) accumulated still more or less visible paleo-shorelines. However, offshore from the equatorial river mouths, particularly the main ones (Congo), pelitic sediments settled in morphological and structural lows. High sedimentation rates were common at the beginning but they decreased during the final part of the transgression. In the tropical region terrigenous fluvial input is considerably reduced but, in their northernmost parts, aeolian contribution of silts and ultrafine sands is recorded in the surficial sediments. Carbonate biogenic deposition The main sedimentary unit of bioclastic origin formed during the first standstill of the Holocene sea-level rise (12,000 y B.P.). It is a belt of Amphistegina sands, recorded on the outer shelf between 80 and 120 m, which represents a fossil fauna. Recent bioclastic sands are more developed in the tropical region, north of the area which has been studied; they are more dependent on structural rocky shoals, than in the equatorial zone where terrigenous influxes impede their development. Glauconite deposition This kind of sediment is characteristic of the equatorial regions where two major conditions were satisfied during the low-stand phase: (1) the presence of faecal pellet substrates due to the increase of primary productivity related to the stronger upwellings and, (2) larger iron input releases by podzolic soil evolution. Northward of the Congo-Gabon shelf, effectiveness of both conditions decreased. Offshore from the Coˆte d'Ivoire, iron was trapped in ferralitic profiles and on the Senegal and Mauritania shelves the green grains are rare and berthierine occurs in a limited time and space range

Typology of nearshore bars in the Gulf of Lions (France) using LIDAR technology

Nearshore bars are generally present on sandy coasts and play a significant role in wave breaking and sediment exchange between beach and shoreface. The study area is located on the Languedoc-Roussillon coast in the Gulf of Lions (southern part of the French Mediterranean coast). This microtidal environment is classified as a wave-dominated coast. The sand coast displays different bar systems (single or multiple; straight or crescentic). The alongshore variability of bar morphology in the nearshore zone was investigated in August 2009 during one week, using a topo-bathymetric LIDAR data set (300 km(2)). LIDAR makes it possible to cover a large area in a very short time with a high resolution. The topo-bathymetric LIDAR offers the added benefit of morphological information about the beach-sea transition in very shallow water (below I in), data often difficult if not impossible to obtain with traditional techniques. The purpose of this paper is 1) to depict the distribution of bars and their characteristics along the 180 km coast of the Gulf of Lions; 2) to update the classifications of sand bars typologies in Languedoc-Roussillon; 3) to pay particular attention to the description of the intricate inner system. Globally, cross-shore distribution of subtidal morphologies is characterized by both an outer and an inner system. The outer system is crescent-shaped in the south and straight in the northern part with a distinctive regional delimitation. The inner system comprises an inner bar and, near the coast, a complex fluctuating bar called Low Bar Beach (LBB). Several intermediate states were identified and added to the new classification proposed in this paper. These results clearly emphasize the importance of LIDAR technology for a better understanding of bar behaviour and single and/or multi-bar beach organisation

Hydrodynamics over a microtidal double crescentic barred beach in low energetic conditions (Leucate Beach, France)

The south part nearshore zone of the Gulf of Lions coast (Mediterranean Sea) is characterized by a double crescentic sandbar system. During the winter 2007, a campaign of intensive hydrodynamical measurements (current profiles) was realized. During this campaign, based mainly on ADCPs, the maximal recorded wave height was 1.5 m. Four events were observed; two of those had northern incidence, one with southern incidence and a last one with frontal incidence. This paper proposes 3D hydrodynamical circulation maps over this microtidal bar system. The currents described reveals rip, bed-return and longshore currents strongly influenced by the wind-waves forcing and the bathymetry. At the apex of the oblique incidence events, the longshore component is the most important. The breaker zone is only located over the inner bar. During storm waning conditions, the cross-shore currents appear over the trough of the outer bar. The hydrodynamic circulation is then compared with other observations made in the literature

The Late Holocene parasequence of the Banc d'Arguin (Mauritania): Role of aeolian detrital inputs in the lithology of shallow water platform parasequences

The Banc d'Arguin (BA - Mauritania) has the double originality of being a shallow water platform (SWP) located on the edge of a sandy desert. This arrangement is rare in the world: Shark Bay in Australia, the western edge of the Persian Gulf and the Namibian margin are the main examples. BA's detailed study both in the marine part of the platform and on the coastal plain has highlighted the peculiarities of the Late Holocene parasequence (LH). In the basin, it is made up of two units recognized in seismic reflection: U5 surmounted by U6 / U7 in lateral variation of facies. U7 also constitutes most of the coastal plain, the construction of which Dia (2013) described in 5 stages. On its arrival, the postglacial Nouakchottian sea invaded areas determined by the construction and progression of ergs during the glacial episode (Azefal to the north, Agneitir and Akchar to the south). Their orientation defined the axes of penetration of the sea in the inter-ergs (Ras el Mâ, sebkha Acheil). In addition, the estuaries of the paleo-wadis, functional during the wettest episodes, were occupied by the sea (Khatt des Ogols). The ingression thus exceeded 12 km in Ras el Mâ and 10 km in the sebkha Acheil. The subsequent development was characterized by the clogging of the bay heads. It mainly used wind sands pushed in the axis of thalwegs and inter-ergs. The stability of the sea level since its arrival at its current level limited accommodation. The accommodation / supply ratio of Cattaneo and Steel (2003) was well below 1. The LH parasequence is therefore generally thin but very extensive on the surface. It is made almost entirely of sandy deposits characteristic of the inter and supratidal coastal environments: beach ridges and sedimentary spits, coastal dunes, large sand-flats which evolved into sabkhas for the oldest, as progradation progressed. The occasional use of the high points of the shore by the Neolithic populations underlined the coastal morphology. The description of the arrangement of the sedimentary subunits formed during the five phases of the period shows that it was formed by progradation with little aggradation during a phase of normal high-level regression.The comparison of the conditions prevailing in the other SWPs identified in the world shows that it is not the transgressive or regressive tendency of the deposits which is their most striking character. The very different lithology of the deposits is more discriminating and underlines the role played by desert sand inputs in the expression or not of other modes of biogenic and/or chemical sediment production. In the case where there are significant wind and fluvial siliciclastic components (northwest coast of Namibia) or significant wind inputs (BA in Mauritania), the production of biogeochemical carbonate components is reduced (Namibia) or even prevented (Mauritania). On the contrary, when the detrital inputs from a nearby desert environment are low (Shark Bay in Western Australia) or inefficient to almost non-existent (west coast of the Persian Gulf), the biogeochemical processes involved in the development of carbonates become predominant and lead to the formation of carbonate platforms. This continuum of models offers the possibility of identifying the amplitude of the desert signature in the paleogeographic reconstructions of certain platforms