This study shows that calcium carbonate plays an important role as a cementing agent of various marine sediments. The measured vane shear strength of marine soil samples is shown to vary with depth and is strongly correlated with the calcium carbonate content. The results show that an increase in calcium carbonate of 1% causes an increase in shear strength of about 10 kPa. Moreover, under accumulating self‐weight, consolidation is found to be enhanced by calcium carbonate. It was also found that both the cementation and condensation due to calcium carbonate are the major factors accounting for the strength development of marine sediments, beside consolidation. These effects are often greater than those due to grain size effects.