Calcareous sediments are types of sedimentary deposits primarily composed of calcium carbonate (CaCO3). These sediments often originate from the remains of marine organisms, such as corals, mollusks, and foraminifera, which accumulate on the ocean floor after they die. Over time, these materials can compact and cement together, forming rock types like limestone. These sediments play a crucial role in the carbon cycle and can influence ocean chemistry. They are commonly found in shallow marine environments, where conditions are favorable for the growth of calcifying organisms. Calcareous sediments can also provide valuable information about past climate conditions and marine ecosystems.