Formation of Accretionary Complexes and Radiolarian Fossils

The geological framework of Japan is made up of accretionary complexes. These are formed when rocks that have accumulated on the sea bed attached themselves on the landward side due to subducting plates. The rocks in these accretionary complexes contain many radiolarian fossils. Radiolarians are zooplankton no bigger than 1mm in size that inhabit the seas. Radiolarians have evolved over time, and the shape of its shells have changed accordingly. It is now becoming possible to determine geological age by extracting the radiolarian fossils from rocks and examining the shape of their shells.