Giant Ooids as One Kind of Anachronistic Sediments in Lower Triassic: A Case Study from Moyang Section, Guizhou Province, South China

摘要

Lower Triassic carbonate ooids are widely distributed all over the world, from northern Italy to Germanic basin, extending across Turkey, Oman, Iran, and finally to Australia. South China and North Vietnam blocks in the paleo-equators in the eastern Tethys are also covered by extensive carbonate ooid deposits of Early Triassic. The oolite starts to develop after the Permian-Triassic mass extinction, and flourishes in the whole Early Triassic. Thus it is regarded as "disaster deposits". However, the Lower Triassic ooids are unusual in their relatively large dimension. Some of them are known as giant ooids, commonly developing in the Neoproterozoic, but rarely after the Cambrian. Because Lower Triassic giant ooids are not a local depositional phenomenon, found at the peripheral belt of the Yangtze platform, the isolated platform in the Nanpanjiang basin (South China), the Yidun block (southwestern China) and the Germanic basin, they seem to be one kind of anachronistic sediments.