Carbonate sediments pelagic

Heat flow affects the rate of alteration of pelagic ooze to chalk the higher the temperature, the greater the degree of cementation of the sediment. This effect on the ooze/chalk transition has been convincingly demonstrated by Wetzel (1989) in a study of compositionally similar pelagic carbonate sediments at DSDP sites 504 and 505 located south of the Costa Rica Rift zone. 

Manghnani M.H., Schlanger S.O. and Milholland P.D. (1980) Elastic properties related to depth of burial, strontium content and age, and diagenetic stage in pelagic carbonate sediments. In Bottom Interacting Ocean Acoustics (eds. W.A. Kupferman and F.D. Jensen), pp. . Plenum Press, New York. 

Seawater Pore water Siliceous oozes Carbonate oozes Pelagic days Clastic sediments Altered basalts Fresh basalts Layer-3 gabbros Continental sediments Sandstones Limestones Shales... 

Calcium carbonate is the most important biogenic component in pelagic marine sediments which cover an area of about 320-10 kml Carbonate-rich sediments (>30 % CaCO ) form about 55 % of the deposits on the continental slopes and the deep-sea floor (Lisitzin 1996 Milliman 1993). A new compilation on the distribution of carbonate-rich pelagic sediments (Fig. 9.2b) has been recently carried out by Archer (1996a). 

Milliman, J.D. and Droxler, A.W., 1996. Neritic and pelagic carbonate sedimentation in the marine environment ignorance is not a bliss. Geologische Rundschau, 85 496-504. 

The matrices and sources of the sediments listed in Table 4.2 are sometimes unclear. Those that are known are highly weighted toward clastic (quartz- and aluminosilicate-rich) marine sediments from coastal environments. Some of these reference materials, such as MESS-3 (NRC-Canada), MAG-1 (USGS) and the Arabian Sea and Pacific Ocean samples (IAEA 315, and 368), could provide excellent examples of clastic marine sediment representing the main repositories of organic matter in the ocean (Hedges and Keil, 1995). The listed materials fail to include both open-ocean opal and carbonate oozes, as well as pelagic red clays. 

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... 

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