Bioreef is a site of the highest diversity of biota on the earth's surface. Geohistorically, however, it was a sort of fairly simple mound in the Precambrian Era as exemplified by a stromatolitic hump. The early Cambrian archaeocyathid reef was monotonous but the first true bioreef made by calcium carbonate-secreting marine animals. The Paleozoic and later coral reefs have been much amplified in their constitutions through ages. It was stressed that the ecological reefs should clearly be distinguished from the stratigraphic ones by paleoecological analysis.
The bioreef is here subdivided into four main ecological types, i.e, the isolated island type, the plateau island type, the continental shelf type and the shelf margin type. They are characterized by respective grades of development of the skirts that frill the reefs. Bioreefs formed on a shallow and wide shelf like the Great Barrier Reef are associated with well-developed inter-reef or back-reef type stagnant basins which bear a high potentiality of metamorphism of the organic materials derived from the reef biota into petroleum. Excretion and bioerosion of reef inhabitants are described as the important agencies of a biochemical activity for destructive and diagenetic processes of the reefs.
Finally, a hypothetical classification of several limestone bodies in Japan is proposed on the basis of paleoecological megastructures of these carbonate sediments.