Sediments pelagic

Froelich, P. M., Klinkhammer, G. P., Bender, M. L. et al. (1979). Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic suboxic diagenesis, Geochem. Cosmochim. Acta 43, 1075-1090. 

Lead isotopes. Sato and Sasaki (1973) concluded on the basis of a remarkable narrow range in lead isotopic composition of Kuroko ores that lead of Kuroko ore came from deep-seated source which originated from subducting pelagic sediments. 

Hole MJ, Saunders AD, Marriner GF, Tamey J (1984) Subduction of pelagic sediments implications for the origin of Ce-anomalous basalts from the Mariana islands. J Geol Soc London 141 453-472 Holland HD (1984) The Chemical Evolution of the Atmosphere and Oceans. Princeton Uiuversity Press, Princeton... 

Newman S, Macdougall JD, Finkel RC (1986) Petrogenesis and °Th- U disequilibrium at Mt. Shasta, Califonua, and in the Cascades. Contrib Mineral Petrol 93 195-206 Nichols GT, Wylhe PJ Stem CR (1994) Subduction zone melting of pelagic sediments constrained by melting experiments. Nature 371 785-788... 

Tsaihwa J. Chow and C. C. Patterson. The Occurrence and Significance of Lead Isotopes in Pelagic Sediments. Geochimica et Cosmochimica Acta. 26 (Feb. 1962) 263-308. 

Clastic and pelagic sediments. Only a handful of clastic and pelagic samples have been analyzed for 5 Mo (Siebert et al. 2003). Clastic sediments (two samples) are indistinguishable from igneous rocks in their Mo isotope compositions. Pelagic clays (two samples) show enrichment in Mo (3.4 and 185 ppm), and also a shift toward lighter d Mo similar to ferromanganese sediments. 

Most of the solid matter found in the sediments of the open ocean was transported to the seafloor via the slow sinking of small particles through the water column. This process is termed pelagic sedimentation. Other types of sedimentation are discussed in the next chapter and include turbidity flows, hydrothermal deposits, and deposition of large animal carcasses, e.g. whales, squid, and fish. 

When particles first become incorporated into the sediments, quite a bit of seawater is usually present between adjacent grains. This is termed pore water or interstitial water. In some cases, it is difficult to define exactly where the bottom of the ocean stops and the seafloor begins, especially if bottom currents are resuspending a lot of particles. As pelagic sedimentation adds particles to the sediment, layers deposited at an earUer time are eventually buried. This produces distinct horizontal layers if the types of particles collecting on the seafloor vary over time. 

Table 12.3 Electron Acceptors in (a) Pelagic Sediments and (b) Continental Margin Sediments. ... 

Many particles reach the seafloor by sinking through the water column. This particle-byparticle accumulation is termed pelagic sedimentation. Sinking rates depend on particle size, shape, and density. The sinking rate of a particle in a fluid experiencing laminar flow can be estimated from Ostwald s modification of Stokes law. 

Table 13.6 Sedimentation Rates of the Noncarbonate Fraction of Pelagic Sediments. ...

The micrometeorites that melt during passage through Earth s atmosphere tend to solidify as spheres. These are termed cosmic spherules. The mineralogy of these spherules is given in Table 13.2. Their high iron and nickel content make them much denser (3 to 6g/cm ) than continental rock ( 2.7g/cm ). Like aeolian particles, cosmic dust deposited on the sea surface eventually settles to the seafloor via pelagic sedimentation. 

The clay minerals of aeolian origin comprise 25 to 75% of the mass of pelagic sediments. The large range in composition reflects the latitudinal nature of the dust belt as well as dilution by other locally important particle types such as clay minerals of volcanogenic origin and biogenic hard parts (calcite and opaline silica). 

The global distribution patterns of kaolinite, chlorite, montmorillonite, and illite in pelagic sediments are listed in Table 14.3 and illustrated in Figures 14.8 through 14.11. 

About 25% of the carbonates deposited in shallow water are eventually eroded and carried downslope by bottom and turbidity currents to become part of the shelf and pelagic sediments. Shallow-water carbonates are also notable for their mineral composition. In addition to calcite and aragonite, some shallow-water calcifiers deposit hard parts containing high percentages of magnesium. These are referred to as magnesium-rich calcites. 

In contrast to calcium carbonate, all seawater is undersaturated with respect to BSi. As shown in Table 16.1, the imdersaturation is very large and increases with depth because the solubility of BSi increases with pressure. Thus, all siliceous hard parts are subject to dissolution. Nevertheless, about 25% of the BSi created in the surfece waters survives the trip to the seafloor via pelagic sedimentation. Direct observations of this transport... 

Schematic longitudinal profile through a semi-isolated basin located in a hot, arid climate and separated from the open sea by a narrow portal. The sill depth, although shallow, is still great enough to permit some two-way flow of surface water. The lines show inferred seawater density (g/cm ) and the arrows show current directions. The pattern of evaporite deposition is based on the relationships between brine density and precipitate composition as shown in Figure 17.1, assuming that salt particles accumulate on the seafloor through the process of pelagic sedimentation. Source-. From Scruton, P. C. (1953). American Association of Petroleum Geologists Bulletin, 37, 2498-2512.

---