Bird’s-Eye Structures in Carbonate Rocks and Their Environmental Significance

Up to date, bird’s-eye structures have long been believed to be characteristic facies criteria for recognition of tidal flat environments including intertidal and supratidal environments.
This paper deals in detail with the bird’s-eye structures identified in the Jipao member of the Middle Devonian Dushan Formation, Guizhou Province. In terms of rock textures, sedimentary structures, palaeontology, sedimentary sequences and palaeogeographic settings, the bird’s-eye structures tend to be ascribed to the semi-enclosed lagoonal environments within the platform facies. Therefore the discovery and experimental study of the structures in modern subtidal environments show that the bird’s-eye structures may be recognized not only in tidal flat environments, but also in some subtidal environments.
The paper also discusses the bird’s-eye structures in the intertidal and supratidal environments in the Upper Devonian Yaosuo Formation, Feifengjing and the Upper Devonian Rongjiang Formation, Buzhai, Dushan, Guizhou. By comparison of the bird’s-eye structures in tidal flat environments with those in subtidal environments, it is possible to distinguish the bird’s-eye structures formed in different environments based on the shapes, genesis and associated rocks, and it is emphasized at the same time that comprehensive environmental analysis should be made by combination with the various facies criteria.