If there had been, there would be no fossils with calcium carbonate shells. (abc.net.au)
When water is undersaturated with respect to calcium carbonate, marine organisms can no longer form calcium carbonate shells (Raven et al., 2005). (ipcc.ch)
The sediments are made up of microscopic calcium carbonate shells and fine - grained clay and silt sediment that is washed in from the nearby European continent. (sciencedaily.com)