Final answer:
Biochemical limestones are primarily made up of the remains of marine organisms such as clams, corals, and algae. These deposits form significant carbon reservoirs and contribute to the global carbon cycle.
Step-by-step explanation:
Biochemical limestones are dominated by carbonate mud and fragments of marine organisms such as clams, corals, foraminifera, and marine algae like coccolithophores. These marine organisms use calcium carbonate (CaCO₃) to create their structures like shells and external skeletons. Over time, as these organisms die, their remains contribute to the formation of sediment on the ocean floor, which under the right conditions, solidify into limestone.
Limestone varieties like chalk consist of microscopic marine animal shells and marine algae, which react with dilute acid by fizzing. This is due to the presence of calcite, a mineral form of CaCO₃, in the limestone. Diverse limestone types, such as oolite and tufa, are formed under varying environmental conditions, from shallow wave-agitated settings to cold spring areas with water rich in dissolved calcium carbonate.
Thus, biochemical limestone is a direct result of biological processes and is a significant carbon reservoir on Earth, contributing greatly to the global carbon cycle.