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Abstract

The sedimentary patterns of Araçá Bay and the adjacent sector of the São Sebastião Channel (SSC) were determined by grain size parameters and carbonate content. The inner bay contains two intertidal flat facies, with very fine to coarse sand and very coarse silt respectively. The outer bay is a subtidal flat facies with unimodal very well sorted and very fine sand. In the adjacent area of the SSC, the central and northern sectors correspond to a sublittoral muddy facies, composed of poorly to very poorly sorted and very coarse to medium silt, and the southern sector corresponds to a sublittoral sandy facies, with very poorly sorted and very fine to coarse sand. The source of sand and very coarse silt are relict terrigenous deposits; coarse silt and medium silt are supplied to the inner bay and the SSC by the intense summer rainfall; and the input of fine and very fine silt is related to suspended sediment from the inner shelf due to storm waves coming from the south. In contrast to seasonal grain size variations in the SSC and the intertidal flat, grain size of the subtidal flat is homogeneous throughout the whole year, denoting an intense sediment transport by local waves and tidal currents. In summary, Araçá Bay is a particular case of sheltered tidal flats, controlled by tides and waves with a minor fluvial influence, but mainly composed of terrigenous sediments. According to this sedimentary characterization, the sensitivity of Araçá Bay to oil spills is reclassified. The practical absence of fine sediments in the subtidal flat determines its low potential to accumulate pollutants, while the intertidal flat and the adjacent SSC present a higher potential. Consequently, this study shows that sensitivity to oil spills of sandy tidal flats and muddy tidal flats must be classified separately. •Five sedimentary facies are defined in Araçá Bay and the adjacent channel.•Sand source is related to siliciclastic relict deposits.•Coarse and medium silt is supply by regional rainfall.•Fine and very fine silt is supplied in suspension from the inner shelf by storm waves.•Oil spills sensitivity is low in the outer bay; high in the inner bay and the channel.

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The analysis of the accurate topo-bathymetric digital elevation model (DEM), the cartography of the submarine sedimentary cover and the monitoring of short (seasonal) and medium-term (2000-2009) morphological changes have permitted depicting the erosional trend in the short and medium-term of the Maspalomas sedimentary system. Short-term analysis showed intense sedimentary fluxes between the beaches and the inner shelf, and sedimentary exchanges with other sectors of the inner shelf, while the steep slope inner shelf fronting La Bajeta cape was identified as a sink area. In the medium-term the sediment budget showed high erosion of the supratidal and intertidal sectors of the beaches due to storm waves in the 2005-2006 winter, followed by accretion over the next four years, but which did not reach the initial sedimentary state. The inner shelf and subtidal sector of the beaches showed negative budgets in the short and medium-term. Interannual variability of the wave and wind regimes determines decadal beach erosion-accretion cycles, while long-term climatic change, evidenced at the study area by a decrease of trade winds and NE wave intensity in 2005, is expected to produce a possible increase of erosion at the El Inglés inner shelf and consequently a decrease in sediment inputs to the El Inglés beach and Maspalomas dune field. Finally, the influence of the geological heritage is depicted by the Fataga gully's control of the present coastal morphology, and by the island relief control of the wind, waves and current directions in the study area.
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Urban effluent discharges in Brazilian coastal areas are a chronic problem and often lead to changes in the quality of the marine environment. São-Sebastião-Channel (SSC) is an important aquatic ecosystem to be monitored for urban sewage contamination due to the intense urban activities in that region, as well as the relative high biodiversity of marine organisms. In the area are present three submarine sewage outfalls, a commercial harbour and also the biggest oil terminal in Brazil. Total organic carbon (TOC), total nitrogen (TN), total sulphur (TS), steroids and linear alkylbenzenes (LABs) were measured in sediment samples collected in three strategic locations of the SSC in order to monitor urban sewage contamination. Total LAB and total sterols levels ranged from below DL-51.3ngg(-1) and below DL-10.40μgg(-1), respectively. Samples collected near sewage outfall in the central part of the SSC had higher concentrations of urban sewage-associated contaminants. Copyright © 2015 Elsevier Ltd. All rights reserved.
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A total of 111 Petersen grab sediment samples, collected during two cruises in 1991 and 1993, on the inner and middle continental shelf between Guanabara Bay and São Francisco do Sul, on the southeastern Brazilian margin, were analyzed for the purpose of understanding the nature and distribution of the organic matter in the surface sediments. The analysis of the distribution of the different parameters related to the organic matter revealed the existence of an important distinction between the sediments to the south and to the north of the São Sebastião Island. Six sedimentary zones characterized by different mean values of the organic matter parameters can be identified. The analysis of the δ13C and C/N ratios distribution suggest an increasing contribution of land derived organic matter toward the north. The distribution of the organic matter in the area can be explained qualitatively by a model of water mass dynamics, which acts over the southeastern shelf of Brazil.
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A bar on the Brazos River near Calvert, Texas, has been analyzed in order to determine the geologic meaning of certain grain size parameters and to study the behavior of the size fractions with transport. The bar consists of a strongly bimodal mixture of pebble gravel and medium to fine sand; there is a lack of material in the range of 0.5 to 2 mm, because the source does not supply particles of this size. The size distributions of the two modes, which were established in the parent deposits, are nearly invariant over the bar because the present environment of deposition only affects the relative proportions of the two modes, not the grain size properties of the modes themselves. Two proportions are most common; the sediment either contains no gravel or else contains about 60% gravel. Three sediment types with characteristic bedding features occur on the bar in constant stratigraphic order, with the coarsest at the base. Statistical analysis of the data is based on a series of grain size parameters modified from those of Inman (1952) to provide a more detailed coverage of non-normal size curves. Unimodal sediments have nearly normal curves as defined by their skewness and kurtosis. Non-normal kurtosis and skewness values are held to be the identifying characteristics of bimodal sediments even where such modes are not evident in frequency curves. The relative proportions of each mode define a systematic series of changes in numerical properties; mean size, standard deviation and skewness are shown to be linked in a helical trend, which is believed to be applicable to many other sedimentary suites. The equations of the helix may be characteristic of certain environments. Kurtosis values show rhythmic pulsations along the helix and are diagnostic of two-generation sediments.
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Two distinct but intergradational types of estuaries (wave- and tide-dominated) are recognized on the basis of the dominant marine process. Wave-dominated estuaries typically possess a well-defined tripartite zonation: a marine sand body comprised of barrier, washover, tidal inlet and tidal delta deposits; a fine-grained (generally muddy) central basin; and a bay-head delta that experiences tidal and/or salt-water influence. The marine sand body in tide-dominated estuaries consists of elongate sand bars and broad sand flats that pass headward into a low-sinuosity ("straight') single channel; net sand transport is headward in these areas. -from Authors
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A shore platform on the western coast of Galicia in northwestern Spain has been inherited from interglacial stages when sea level was similar to today. The wide, gently sloping intertidal platform is backed in places by supratidal rock ledges, and in other places by a steeper and narrower supratidal ramp. The gradient of the intertidal platform is consistent with the relationship between platform gradient and tidal range, but the slope of the ramp is much too high. The abandoned and degraded sea cliff is grass-covered along most of this coast, and the ledges and the ramp, which extend up to several metres above the highest tides, are covered by lichen and, in places, by salt-tolerant plants. Radiocarbon-dated sediments in the cliff, which range up to 36 000 years in age, lie on top of an ancient beach deposit. The former beach, remnants of which are found in situ on the ramp and rock ledges, as well as two caves that are filled with the dated sediments, are probably last interglacial in age. The morphological and sedimentary evidence suggests that the supratidal ramp and ledges were also formed during the last interglacial stage, whereas the wider intertidal platform is probably the product of several older interglacials, when sea level was generally similar to today. A general model is proposed for the inheritance of shore platforms in macro- and microtidal environments. Copyright © 1999 John Wiley & Sons, Ltd.
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Grain size analysis is an essential tool for classifying sedimentary environments. The calculation of statistics for many samples can, however, be a laborious process. A computer program called GRADISTAT has been written for the rapid analysis of grain size statistics from any of the standard measuring techniques, such as sieving and laser granulometry. Mean, mode, sorting, skewness and other statistics are calculated arithmetically and geometrically (in metric units) and logarithmically (in phi units) using moment and Folk and Ward graphical methods. Method comparison has allowed Folk and Ward descriptive terms to be assigned to moments statistics. Results indicate that Folk and Ward measures, expressed in metric units, appear to provide the most robust basis for routine comparisons of compositionally variable sediments. The program runs within the Microsoft Excel spreadsheet package and is extremely versatile, accepting standard and non-standard size data, and producing a range of graphical outputs including frequency and ternary plots. Copyright © 2001 John Wiley & Sons, Ltd.
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Sedimentological parameters of 206 box-core tops and 387 van Veen grab samples were analysed so as to understand the distribution, source and sedimentation rates in the shelf and upper slope of the southern Southeastern Brazilian margin.Most of the parameters (bulk organic matter constituents, δ13C, and εNd) can be grouped on northern and southern sectors, separated by a sharp boundary. This suggests that sediment sources and sedimentary processes are different in both regions.The southern sector of the study area is more influenced by cold waters coming from the southern portion of the South American shelf and the organic fraction revealed an important role played by the primary productivity in the sedimentation. Also, εNd values indicate that part of the inorganic fraction of the southern sector sediments are allochtonous, probably coming from younger rocks of the Andean chain probably reaching the shelf through the La Plata river runoff.In the northern part of the study area the sedimentation is controlled almost exclusively by the meandering of Brazil Current. Compositional and isotope bulk organic parameters showed a more complex mixing of terrigenous and pelagic fractions. Also, εNd values are associated with the precambrian rocks of the Brazilian shield.The whole area exhibits sedimentation rates, varying from 5 to 660 mm kyr−1.
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Sediment erosion results from hydrodynamic forcing, represented by the bottom shear stress (BSS), and from the erodability of the sediment, defined by the critical erosion shear stress and the erosion rate. Abundant literature has dealt with the effects of biological components on sediment erodability and concluded that sediment processes are highly sensitive to the biota. However, very few sediment transport models account for these effects. We provide some background on the computation of BSS, and on the classical erosion laws for fine sand and mud, followed by a brief review of biota effects with the aim of quantifying the latter into generic formulations, where applicable.
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The application of an integrated data analysis and modeling scheme reveals that decadal-scale shoreline evolution along a U.S. Pacific Northwest littoral cell is highly dependent on both sediment supply and wave climate variability. In particular, accurate estimates of (Columbia River) sediment supply and sediment feeding from the lower shoreface are critical components of balancing the barrier beach sediment budget and are therefore essential to making sensible shoreline change hindcasts and forecasts. A simple deterministic one-line shoreline change model, applied in a quasi-probabilistic manner, enables evaluation of the influence of sediment supply and wave climate variability through simulation of historical shoreline change. Through iteration, a range of realistic scenarios are developed to constrain decadal-scale shoreline change predictions. Modeled shoreline changes are significantly sensitive to directional changes in the incident waves, and therefore sensitive to the occurrence of interannual climatic fluctuations such as major El Niño events. A predicted increase in the intensity of the east Pacific wave climate (1.0 m increase in significant wave height in 20 yr) affects forecast shoreline positions only when this increase occurs during the winter storm season. However, the effect of this increase in storm power during any given year is small relative to the impact of major El Niño events. The model has significant skill in decadal-scale hindcasts suggesting that alongshore gradients in sediment transport dominate coastal change at this scale at this site. However, both data and model results suggest that net onshore feeding from the lower shoreface is responsible for approximately 20% of the decadal-scale coastal change. Field measurements and poor model skill at annual scale indicate that cross-shore processes likely dominate coastal change at shorter time scales.
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