The following poem describes a sea of clouds, a waterfall and a cave.

A, there is no new substance generated in the sea of clouds in Huangshan, which belongs to physical changes, so A is wrong;

B, Huizhou stone carving is only a change of shape, which belongs to physical change, so B is wrong;

C. The changes during the formation of Taiji Cave in Guangde are: calcium carbonate reacts with water and carbon dioxide to generate calcium bicarbonate, and calcium bicarbonate decomposes to generate calcium carbonate, water and carbon dioxide, so it belongs to chemical changes, so C is correct;

D. The Dabie Mountain Waterfall is just the flow of water, and there is no new substance generated, which belongs to physical changes, so D is wrong.

So choose C.