Ministromatolite Modular Reef Framework, ~1.5 Ga, Yesanpo, North China.

Earth's earliest known framework reef, ~1500-million-year-old Yesanpo Mound in the Wumishan Formation, North China, consists of columns and cones built by innumerable conjoined originally aragonitic ministromatolites, each ≤ 2 cm wide. The Mound contains numerous irregular, decimetric, cavities. These are now filled with carbonate mud, giant ooids, and originally aragonitic marine cement. The role of ministromatolites in constructing this modular framework very broadly resembles that of polyps in present-day scleractinian coral colonies. Yesanpo Mound preserves geochemical signatures and traces of organic filaments consistent with suboxic conditions, yet it predates the earliest reported reef-dwelling animals by ~600 Myr. Similar spaces in reef framework may have provided ideal habitats for cryptic biota during the late Proterozoic. These are prime targets in the continued search for early animal life.