See reef 890. Fossils of Actinacis and
Spiroclypeus were found at 1245 m and 1255 m in core XK-1, supporting the estimate that these biogenic reefs date back to the late Oligocene. Besides the
two fossils, red algae, including Lithoporella melobesioides, Lithoporella minus, Neogoniolithon,
and Mesophyllum, and benthic foraminifera, including Amphistegina lessonii, Amphistegina lobifera, and Spiroclypeus were also found in the lower part of the Sanya Fm.