Sediment Depositional Processes Research Articles

Distributed Parameter Modeling of Sediment Movement and Particle Size Distributions

ABSTRACT A spatially descriptive erosion submodel for estimating the particle size distribution of eroded sediment from disturbed upland watersheds and construction sites has been developed and incorporated into the ANSWERS watershed model. Model validation is accomplished using data from field plot studies. The model's usefulness as an erosion control planning tool is demonstrated on a construction site in central Indiana. The model divides the watershed into a uniform grid of square planar elements. Within each element, the model describes the processes of interception, infiltration, surface storage, surface flow, subsurface drainage, and sediment detachment, transport and deposition. The continuity equation is then used to integrate the individual elemental responses into a system response that describes the watershed as a whole. The erosion process is limited to the overland flow regime.

Conjunctive use of deterministic and stochastic models for predicting sediment storage in large reservoirs: 2. Deterministic model for the sediment deposition process

The papers presented discuss the development of a model to predict the deposition of sediment in reservoirs as a function of time (in years). The papers consist of three parts which are published together: Part 1 dealt with the development of the stochastic model for the total deposition of sediment in reservoirs. This cumulative deposition of sediment in time was shown to be an additive process defined on a finite Markov chain. The model was analysed to obtain the mean and the range of the cumulative sediment deposition as a function of discrete time in years. The present Part 2 discusses a deterministic model for the deposition process along the length of the reservoir. The pattern of deposition is a function of the inflow and the concentration of sediment in the inflow as well as the initial level in the reservoir and the initial composition of the sediment. The inflow in the reservoir is treated as unsteady and non-uniform. As much of the physical characteristics of the reservoir as possible is included in the analysis. Part 3 discusses the application of the two models in conjunction to the John Martin Reservoir, Bent County, Colorado, for which measurements are available (though limited in extent). The comparison between results obtained from the model and the actual measured data is found to be in good agreement with each other. The symbols used and references are provided separately in the Notation and References Section of each part.

North Brazilian Ridge and Adjacent Continental Margin

geologic and geophysical reconnaissance of the continental margin of the north coast of Brazil led to the discovery of a narrow basement ridge, herein called the North Brazilian Ridge. The ridge closely parallels the coast of Brazil between the Amazon cone and the easternmost tip of Brazil and is essentially a continuous topographic and/or structural feature across a distance of 1,300 km. The ridge lies 150-200 km seaward from the base of the continental slope. Its topographic relief ranges from about 300 m to about 4 km. Although a conspicuous sediment ponding is observed on the continental side of the ridge, there is no marked contrast in type for the upper few meters of sediment in piston cores from opposite sides of the ridge. The primary process of sediment transport and deposition thus appears to be acting parallel with the ridge rather than downslope. prominent acoustic reflector, which may be synchronous with Horizon A in the North Atlantic, abuts the north flank of the ridge. This observation, together with ages extrapolated from sedimentation rates determined on the ridge at JOIDES drill sites 25-25A, suggests that the ridge is relatively old, of the order of 100 m.y. The ridge is gravimetrically compensated, and gravity values are roughly the same in the basins on opposite sides of the ridge. Magnetic anomalies over the ridge are typically of low amplitude and have an apparently random character. Rock outcrops were photographed along the steep flanks of the ridge and are very similar to outcrops of mafic igneous rocks on the flanks of the Mid-Atlantic Ridge. The North Brazilian Ridge is not continuous with the major fracture zones of the equatorial Atlantic. collective examination of all data leads us to the conclusion that the ridge probably formed by oceanic volcanism shortly after the separation of Africa and South America. Its location and extent may be the direct consequence of the manner and geometry of the opening of the equatorial South tlantic Ocean.

ANÁLISE DA QUALIDADE DA ÁGUA POR METODOLOGIA ESTATÍSTICA MULTIVARIADA NA REPRESA VELHA (CEPTA/IBAMA/PIRASSUNUNGA/SP)

Inúmeras questões de difíceis soluções surgem durante as fases de planejamento, construção e pós-construção de reservatórios que necessitam serem abordadas de forma interdisciplinar, destacando-se dentre estas o processo de deposição de sedimentos. Com a finalidade de analisar o comportamento deposicional de um conjunto de variáveis em represa, este trabalho foi executado, durante os anos de 1998 e 2000, na represa Velha, no Centro de Pesquisa e Gestão de Recursos Pesqueiros Continentais (CEPTA/IBAMA), município de Pirassununga (SP). Esta represa abastece 128 tanques e viveiros para piscicultura, onde foram estabelecidos 6 pontos de coletas de amostras de água, realizadas nos períodos seco e chuvoso. Algumas variáveis quanto à qualidade das águas foram determinadas nas amostras coletadas. Os dados foram submetidos ao método estatístico multivariado da análise de agrupamentos demonstrando que no período seco, os parâmetros tiveram comportamento diferente daquele encontrado para os mesmos parâmetros no período chuvoso. Neste último, apesar do número de agrupamentos ser o mesmo do período seco, ocorrem alterações quanto à natureza dos parâmetros agrupados. Assim, os radicais fosfatos e fósforo total se relacionam diretamente com o material de suspensão no período seco, o mesmo não observado no período chuvoso. O efeito deposicional neste foi mais disperso entre os pontos de coleta em relação àquele verificado no período seco.

Physical Characteristics of Fluvial Deposits: ABSTRACT

The physical processes of sediment transport and deposition by confined unidirectional flow are produced only in a fluvial environment. The physical properties resulting from these processes provide unique criteria for recognition of fluvial deposits. Characteristic physical properties include (1) surface texture, (2) particle shape, (3) texture, (4) fabric, (5) sedimentary structures, (6) bedding, (7) sequence of structures, bedding, and textures, (8) scour surfaces, and (9) local and regional geometric patterns. Other aspects, including mineralogy, detrital clasts and fragments, physical character of the associated sediments, and fauna and flora, may aid in the identification of fluvial environments. Point-bar deposits resulting from channel migration are the most commonly preserved type of fluvial sandstone bodies. These geomorphic features are nearly universal in all meandering streams, and they control clastic deposition. The commonly developed sequence of festoon, current-laminated, and ripple cross-bedded sedimentary units is developed in response to flow across point bars. Other types of fluvial sand bodies, such as those deposited in alluvial fans, braided streams, and deltaic distributaries, exhibit many fluvial characteristics, but they lack the sequence of sedimentary structures related to point-bar deposition. Unidirectional currents produce characteristic grain-size distributions, which suggest a predominance of saltation and suspension modes of particle transport. Current transport produces elliptical-shaped particles with smooth surfaces. Detrital clay clasts commonly are preserved, many altered to clay-ironstone concretions. Minerals chemically stable in fresh, oxidizing, slightly acid water are commonly characteristic, such as kaolinite, feldspar, and ferric iron. The absence of other minerals such as calcite, glauconite, and ferrous iron compounds is significant. The external geometry of fluvial deposits is probably the least characteristic physical attribute. Individual outcrops may not show channeling, and fluvial sand bodies may be of a blanket type. Boundaries of channels, however, show abrupt pinchouts, commonly within a few hundred feet. Trends of sand bodies in connection with paleocurrent and slope indicators provide strong supporting evidence for identifying fluvial environments. End_of_Article - Last_Page 747------------

Deep-Sea Fans in Permian Delaware Mountain Group, Delaware Basin, West Texas and New Mexico: ABSTRACT

Ancient deep-sea fans, consisting of channel, overbank, and fringe deposits, are recorded in the Permian Brushy Canyon, Cherry Canyon, and Bell Canyon Formations (Guadalupian) of the Delaware basin. Sediment economics and depositional processes that characterized the Delaware basin were very similar to those operating in modern continental borderland basins off southern California. Margins of the Delaware basin were incised by numerous submarine canyons. During times of low-standing sea-level, concurrent with glaciation, large volumes of clastic sediment were prograded across constricted shelf lagoons, swept into heads of submarine canyons by longshore and tidal currents, and introduced into the Delaware basin through the channel-levee-over-bank system. Carbonate production and reef growth ceased on the outer platform. As sea-level rose during de-glaciation, shelf lagoons expanded and the volume of clastic sediment reaching the outer platform progressively diminished; carbonate production and reef growth resumed. Basinward from the margin, where channels are narrow and deeply incised, channel width increases and amount of incision decreases. Major flow units (3-10 feet thick), restricted to deep-sea channels, commonly consist upward from the base of the following units: (a) massive, (b) large current-ripple cross-bedded sets (sand waves), (c) plane-parallel-laminated sandstone, (d) small current-ripple cross-bedded sets, and (e) plane-parallel laminae consisting of sandstone, siltstone, and shale laminae. Both large and small ripples consist predominantly of climbing End_Page 471------------------------------ ripples (ripple drift). Minor flow units (less than 3 feet thick), consisting of many different combinations of massive, laminated, small current-rippled, and silty or shaly intervals, are found in channels, over-bank deposits, and as a peripheral aureole of fringe deposits. Flow-unit thickness, velocity, and distance of travel were controlled by the volume of sediment initially released as cataclysmic avalanches and mud flows in submarine canyons. End_of_Article - Last_Page 472------------

Clay Mineral Diagenesis in the Rappahannock Estuary: An Explanation

Mineralogical changes observed in bottom sediments along the Rappahannock salinity gradient include: (1) decrease in kaolinite, (2) decrease in dioctahedral vermiculite, (3) increase in illite, (4) appearance of thermally stable chlorite, and (5) appearance of clay-sized feldspar. All of these changes are real. They correlate with increase in bottom water salinity from 0 to 20%, increase in bottom sediment pH from 5.5 to 7.8, change in grain size distribution, and change in adsorbed ion populations. In the critical area the bottom sediments lose clay by selective sorting and become more silty. The adsorbed ions are Ca and Al in fresh water, Ca and Na with minor K at low salinities, and Na and Ca with major fractions of exchangeable K and Mg at high salinites. Studies of the suspended sediments over a period of years reveal that illite, vermiculite, kaolinite, and clay-sized feldspar are the normal constituents in the load of the fresh water stream. No mineralogical segregation, by differential flocculation for example, occurs during transport of this suspension along the salinity gradient. The increase in illite and feldspar content of the bottom sediments is due to normal processes of sediment deposition. The high kaolinite and dioctahedral vermiculite contents of fresh water bottom samples is due to two possible causes. (1) Samples are obtained from drowned, Pleistocene-weathered, terrace materials that possess this basic mineralogy. (2) Bedload sediment with kaolinite-dioctahedral vermiculite mineralogy is deposited in the fresh water region. Thermally stable chlorite is generated in the saline environment, probably from vermiculite. Simple ion exchange is insufficient to generate the chlorite. It forms by diagenesis.