Where is limestone deposited?
Limestone is a sedimentary rock rich in the mineral calcite, which is made of calcium carbonate. Franciscan limestone is formed mostly from the tiny carbonate shells of single celled marine animals called foraminifera. This type of limestone forms in ocean settings where there is not enough continental mud to dilute the slow “rain” of carbonate shells, and where the ocean is not so deep that all calcium carbonate dissolves into the water before it can be buried in the sediment to form rock. In today’s oceans, all calcium carbonate dissolves below the depth (called Carbonate Compensation Depth or CCD) of about 4 km. Franciscan limestone is thought to have formed on the tops and sides of underwater volcanoes in water less than 4 km deep.
