Sedimentation undisturbed

Most commercial marine diatomite deposits exploit accumulations resulting from large blooms of diatoms that occurred ia the oceans during the Miocene geological epoch. Diatomite sediments older than the Jurassic period are rare in the fossil record. Commercial deposits of diatomite are accumulations of the fossil skeletons, which can occur in beds as thick as 900 m in some locations (5). Marine deposits must have been formed on the bottom of protected basins or other bodies of quiet water, undisturbed by strong currents, in an environment similar to the existing Santa Barbara Channel or Gulf of California (3,6). 

Solution of equation (10) which involves sedimentation in the presence of mixing and that of equation (11) which contains the sedimentation term only, are exponential in nature. The major conclusion which arises from this is that the logarithmic nature of the activity-depth profiles by itself is not a guarantee for undisturbed particle by particle sediment accumulation, as has often been assumed. The effects of mixing and sedimentation on the radionuclide distribution in the sediment column have to be resolved to obtain pertinent information on the sediment accumulation rates. (It is pertinent to mention here that recently Guinasso and Schink [65] have developed a detailed mathematical model to calculate the depth profiles of a non-radioactive transient tracer pulse deposited on the sediment surface. Their model is yet to be applied in detail for radionuclides. )... 

The advent of new techniques to collect undisturbed sediment cores, with well preserved sediment - water interface has brought into sharper focus the various deep sea sedimentary processes, their rates and their effects on the preserved records. As mentioned earlier, recent studies have shown that the record contained in sediments is not a direct reflection of the delivery pattern of a substance to the ocean floor as has so far been assumed the record is modified as a result of several complex physical, chemical and biological processes. Therefore, information on the temporal variations in the tracer input to oceans, if sought, has to be deciphered from the sediment-residuum. In the following we consider one specific example of retrieval of information from the sediment pile the application of deep sea sediments to obtain historical records of cosmic ray intensity variations. 

The close association of the lake sediment geochemistry with SIC rocks and Ni mineralization indicates that the OGS protocol of sampling a discrete depth interval of deeper sediments is successful in obtaining relatively undisturbed and uncontaminated sediments in the vast majority of cases. 

We studied two sites of samples. Firstly, the element s distribution in the ferromanganese nodules and adjacent bottom sediments has been investigated after undisturbed sampling by grabs. Secondly, dimension distribution of discoid, plate, and ellipsoid nodules, as well its fragments and crusts discovered after seagoing dreged samples. 

A variety of human activities increase erosion and sedimentation rates. For example, soil typically erodes from cultivated land five to 10 times as fast as from noncultivated land. Construction sites lose soil 100 times as fast and mined land more than 500 times as fast as land that is undisturbed. Besides greatly increasing water pollution, this erosion accelerates the loss of valuable farmland. By some estimates, as much as 3.3 billion tons (3 billion metric tons) of topsoil is lost to such processes in the United States each year. Overall, the major anthropogenic sources of erosion (and, as a consequence, sedimentation) are certain types of agriculture (such as row cropping), livestock operations, logging, flooding from developed land, and construction projects. 

Alum and lime are added to the water in the tank. The small particles and suspended particles come together or coagulate. If the water is left undisturbed for some time, these particles settle down as sediment. 

The power-time curves (PTCs) obtained with microcosms experimentally enriched and composed of undisturbed cores of sediment and water are highly reproducible (Fig. 2). 

Evaluations of various soil and sediment samplers have been reported [56, 57]. The sediment shovel proved highly practical, but was limited because small particles tend to be lost when the shovel is lifted [56]. A cryogenic sediment sampler was less convenient to use, but allowed the collection of almost undisturbed samples. Houba described a different device for the automatic subsampling of soil, sediment and plant material for proficiency testing [57]. In another study, Thoms showed that freeze-sampling collects representative sediment samples, whereas grab-sampling introduces a bias into the textural composition of the 120 mesh fraction, due to washout and elutriation of the finer fractions [58]. 

Vink, J.P.M. and S.E.A. Vanderzee (1997). Effect of oxygen status on pesticide transformation and sorption in undisturbed soil and lake sediment. Environ. Toxicol. Chem., 16 608-616. 

Seybold, C.A., W. Mersie, C. McName, and D. Tierney (1999). Release of atrazine (14C) from two undisturbed submerged sediments over a two-year period. J. Agric. Food Chern., 47 2156-2162. 

Sampling device operated using a boat-mounted winch that allows collection of a relatively undisturbed surface sediment sample. Essentially, a set of "jaws" with a trigger that closes the sampling device on impact. Volume 2(10). 

Numerous volcanic centres occur on the seafloor of the Sicily Channel (Fig. 8.1). Calanchi et al. (1989) recognised at least ten recent submarine volcanoes of various dimensions, mostly located along NW-SE regional faults. Some of these volcanoes have erupted during historical times others are covered by undisturbed Pliocene-Quaternary sediments and have been detected by seismic profiles and magnetic survey (Allan and Morelli 1971). 

If this newly created ocean were left undisturbed for a few hundred million years, its waters would evaporate and be transported onto the continents in the form of precipitation streams would transport their loads into it. The sediment created in this ocean would be uplifted and incorporated into the continents. Gradually, the influence of the continental debris would be felt and the pH might shift a little. Iron would be oxidized out of the ferrous silicates to make iron oxides, but the water composition would not vary a great deal. 

The next site, containing undisturbed sediments, is the fissure named locality no. 9 of Siitto, which was discovered by quarry-master Andras Schenk in the middle of... 

A number of recent trend studies are summarised below. Settled sediments from lakes and undisturbed (preferably anoxic) sediments represent a historical record of contaminant... 

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