EFFECTS OF CARBONATE ON SEABED FORMATION

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The mechanism of cementation in soils has not been well understood. The lack of information on the cementation prevents from the further progress of geotechnical engineering and better understandings of diagenesis process in geology and sedimentology. In this study, effects of carbonate on the formation of seabed, in relation to strength development, is mainly investigated. In order to find carbonate-cementation development of seabed, carbonate content, shear strength and physical properties such as water content, specific gravity, water content, void ratio, grain size distribution, etc., were measured on the samples obtained from various sites, such as Tokyo bay, Sagami bay, Suruga bay, Osaka bay, Kagoshima bay and seto inland sea. The correlations between these factors show that the cementation of seabed is mainly due to the contained carbonate. It is found that the deviation of strength with depth is mainly dependent on the variation of calcium carbonate content. Furthermore, it is found that the calcium carbonate can promote consolidation of seabed by the aggregation effects.From the geochemical and geological points of view, the sedimentation rate of soil particles can be predicted from the calcium carbonate content. This prediction method needs an assumption that calcium carbonate precipitates on the sea bottom with a constant rate. In this study, the precipitation rate of calcium carbonate obtained is 0.95 g/cm^2/1000y. In the comparison using various methods, the prediction of sedimentation rate obtained from the carbonate method accords with those obtained from ^<14>C and key bed methods, but not from ^<210>Pb method.