Calcareous sediments

Dean WE, Jr. Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss on ignition-comparison with other methods. J. Sediment. Petrol. 1974 44 242-248. 

Neogene calcareous sediments were recovered from the hole 704 of the Ocean Drilling Program in the South Atlantic. The 8lsO of pelagic foraminifera have been analyzed at 82 different depths z reported in meters below seafloor (mbsf) by Hodell and Cieselski (1991) (Table 5.7 and Figure 5.6). 

In the preceding sections, we have discussed the marine processes that control calcium carbonate s formation, dissolution, and delivery to the seafloor. Their combined effects determine the geographic distribution of calcium carbonate in marine sediments seen in Figure 15.5. As noted earlier, the global distribution of calcareous sediments does not seem to follow that of plankton production. This points to the overriding importance of the processes that control the dissolution and sedimentation of calcium carbonate. 

The behaviour of landfill liners with respect to metal sorption has also been investigated by the novel technique of combined sequential extraction-sorption isotherm analysis (CSSA) (Salim et al, 1996). The study demonstrated that Pb and Ni would be effectively immobilised by the clayey calcareous sediment studied, but Cr would not. Roehl and Czurda (1998) applied a similar approach in their investigation of clay landfill liners and showed that speciation was dependent on heavy metal load, with weaker binding at higher concentrations of Cd and Pb. 

Figure 5.2. Grass bed calcareous sediment of Table 5.1, Ferry Reach, Bermuda size grade > 4 mm. (After Pestana, 1977.)...

The thermal conditions at site 504 are very different from those at site 505 (Table 8.4). Physical property measurements at both sites reveal systematic downhole changes and differences between the trends for the two sites. For example, Figure 8.18 shows the porosity-depth curve for the sediments at sites 504 and 505. It is evident that the porosity decreases more rapidly in the higher temperature site 504 calcareous sediments than in the lower temperature site 505 sediments. As would be anticipated from the porosity trends, the compressibility of the sediments decreases systematically with increasing depth. At a similar depth below the sea floor, site 505 sediments are more compressible than those at site 504. All the sediments are over-consolidated, a result of diagenetic cementation. 

These differences in the physical properties of pelagic calcareous sediments at DSDP sites 504 and 505 are a result of the temperature difference between the two sites. A more rapid decrease in diagenetic potential is favored by increasing sediment temperature. The rates of the diagenetic solution-precipitation reactions are increased because of the higher temperature (Baker et al 1980), and the accompanying increased concentrations of ions involved in cementation (Mottl et... 

Figure 8.19. Calculated cement volumes for DSDP sites 504 and 505 calcareous sediments. In the high heat flow area of site 504, cementation starts at a shallower depth and a larger cement volume is observed than at the "cooler" site 505. (After Wetzel, 1989.)...

Inorganic carbon sedimenting and accumulating on the sea floor is mainly as CaCC>3 little dolomite is forming today, and the average Mg content of modem calcareous sediments is about 0.7%, representing a flux of MgC03 to the sea floor of 3 x 1011 moles yl. The Ca2+ for precipitation comes both from rivers and reactions at the sea floor between basalts and sea water, discussed later in this chapter. The overall reaction is ... 

Chave K.E. (1954b) Aspects of the biogeochemistry of magnesium 2. Calcareous sediments and rocks. J. Geol. 62, 587-599. 

The graywacke and quartzite cobbles used for tool making were probably obtained locally from the storm beaches immediately below the coastal sites. Conversely, chert or quartz crystals have not been found on coastal beaches or adjacent regions, despite intensive survey. Although potential chert-bearing calcareous sediments are located inland, no source is known to exist in this region of southern Portugal (5). 

Wollastonite is common in thermally metamorphosed impure limestone and can occur in contact-altered calcareous sediments. In most occurrences, it has been formed as a result of the reaction... 

Figure 14.3. Particle size distribution, (a) Discrete and continuous cumulative particle size distribution, (b) Discrete and continuous particle size distribution, (c) Volume distribution plotted in accordance with equation 3. (d) Particle size distributions at four depths in a calcareous sediment from west equatorial Pacific Ocean, 1°6.0 S, 161 36.6 E, box core No. 136, water depth 3848 m. (From Lerman, 1979.)...

Alexandersson, E.T., 1975. Etch patterns on calcareous sediment grains petrographic evidence of marine dissolution of carbonate minerals. Science, 189 47—48. 

At shallow depths carbonate cements may cause sands to become brittle and hard. Carbonate which precipitates on the sea floor may also form hard grounds in dominantly clastic sequences. Sandstones may become calcite cemented due to dissolution of biogenic aragonite at relatively shallow depth (less than a few hundred meters). Calcareous sediments flushed by meteoric water at shallow depth or exposed during regression may become rapidly ce-... 

Ringrose, S., Kampunzu, A.B., Vink, B.W., Matheson, W. Downey, W.S. (2002) Origin and palaeo-environments of calcareous sediments in the Moshaweng dry valley, southeast Botswana. Earth Surface Processes and Landforms 27, 591-611. 

Scanning electron micrographs of lacustrine calcareous sediments. 

Michard, G. (1971). Theoretical model for manganese distribution in calcareous sediment cores. J. Geophys. Res. 76, 2179-2186. 

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