La marge continentale sud-portugaise: évolution structurale et sédimentaire

The structural and sedimentary evolution of the portuguese continental margin South of Setúbal Canyon is outlined from the study of many seismic reflection profiles and rocks samples. During Triassic and Early Liassic time, a distension affects the Algarve margin that belongs to the Mesogean area. Off Baixo Alentejo rifting phases at Late Jurassic and Early Cretaceous times induced opening or widening of the adjacent part of the Atlantic ocean. Alpine orogeny is inferred to explain the Eocene and Miocene deformation of the margin specially along the main NE-SW fractures

Late Quaternary Halimeda bioherms and aragonitic faecal pellet-dominated sediments on the carbonate platform of the Western continental shelf of India

The Fifty Fathom Flat is a drowned carbonate platform located on the outer continental shelf of western India. It is unique because the carbonate depositional environment prevailed until Early Holocene in spite of its proximity to a major siliciclastic tidal embayment. Study of the bathymetry, seismic and sonograph data together with the petrology, mineralogy and geochemistry of the carbonate sediments and limestones recovered from the platform resulted in (a) the discovery of Late Quaternary Halimeda bioherms and (b) aragonitic faecal pellet-dominated sediments. Echograms reveal buried pinnacles between 62 and 38 m and exposed 2 to 14 m high pinnacles between 65 and 85 m on the platform. These pinnacles occur as narrow to broad mounds (bioherms) in seismic profiles and as linear ridges and massive structures in sonographs. Seismic profiles also show a prominent reflector about 25 m below the sea bed identified by boreholes as a Late Pleistocene erosion surface. The platform consists of relict carbonate sands and limestones. Rounded and ovoid to ellipsoidal aragonite grains are predominant in the sediments. SEM studies indicate elongated parallel canals and crescent to hook-shaped canals, corresponding to faecal pellets, occur in some grains. Algal grains and pellets enclosing algal fragments are also present. The grains in the limestones are similar to those in the sediments. Halimeda and crustacean faecal pellets are abundant components, with minor echinoid, mollusc and benthic foraminifera. The limestones are characterised by abundant pores, dissolution cavities, relic aragonite needles, meniscus cements and drusy calcite fill the pores produced by dissolution of aragonite needles. These features indicate vadose diagenesis. The stable isotopes of the carbonate sands and limestones are almost identical and similar to isotope values of beachrocks of the Red Sea. The limestones ages (8400-9200 yr B.P.) lie within the same age limits (10,400-8300 yr B.P.) as the surficial sediments. It appears that fluvial sediments largely accumulate in the inner shelf and did not hinder carbonate growth on the platform, lying on the outer shelf. We presume that arid climate and nutrients brought by river runoff and shelf edge currents favoured the growth of algal bioherms dominated by Halimeda between 13,700 (?) and 8300 yr B.P. The absence of Late Holocene and modern carbonates on the platform may be due to the combined influence of climatic change, upwelling and neo-tectonic activity at about 9000 yr B.P. The bioherms dominated by Halimeda, produced abundant aragonite muds. Deposit feeding crustaceans and other invertebrates subsequently excreted these muds as faecal pellets. The platform thus contains faecal pellet-dominated sediments

La dynamique des masses d'eaux et des matieres en suspension en Manche Orientale

The structuration between nearshore and offshore waters along the macrotidal French Eastern Channel coast is demonstrated by longitudinal and vertical continuous recordings of salinity, temperature, turbidity and fluorimetry. The distribution of suspended particulate matter, one dissolved marker ( super(125)Sb) and particulate markers (such as diatoms) indicates the variability of the waters from coast to open sea. Semidiurnal and semilunar tidal cycles induce the birth and the evolution of frontal structures along shore-lines with or without estuaries. The hydrodynamic consequences for suspended matter fluxes are presented

Le "fleuve cotier": Un phenomene hydrologique important en Manche orientale. Exemple du Pas-de-Calais

The English Channel has a "megatidal" regime: in the Dover Strait, the tidal range varies between 3 and 9 m in neap-tide and spring-tide respectively. The tide currents are alternating and essentially parallel to the coast. Along the French coast, the fluvial supplies, distributed from the Bay of Seine to Cape Gris-Nez, generate a coastal water mass which drifts nearshore, separated from the open sea by a frontal area: this coastal flow is characterized by its freshness, turbidity, phytoplankton richness, and pollution content. Its width is only 3 to 5 miles, but because of the high concentrations of dissolved and suspended components, it is possible that the coastal flow plays an important role in the fluxes between the Eastern Channel and the North Sea

Annotated record of the detailed examination of Mn deposits from DSDP Leg 48 (Holes 400A, 401, 402)

Unlike many cruises of the Deep Sea Drilling Project, Leg 48 was scientifically planned to drill a number of sites to systematically address the problems of passive margin evolution. Site 400 was drilled at the foot of the Meriadzek Escarpment of North Biscay in 4399 meters depth. The site was located in a half-graben forming part of a succession of tilted and rotated fault blocks near the continent/ocean boundary. Site 401 was situated on the planated edge of a tilted fault-block underlying the southern edge of the Meriadzek Terrace on the north Biscay margin. Site 402 was located on the upper slope of the northern continental margin of the Bay of Biscay. The main objectives were to establish the presence or absence of shallow water Upper Cretaceous beds, and to penetrate pre-Aptian synrift sediments and the upslope equivalent of the deep water Albian-Aptian carbonaceous mudstones penetrated at Hole 400A