Palaeoenvironmental distribution of Ordovician dasycladaleans in the Tarim Basin, Xinjiang, China

Dasycladalean calcified green algae are common in the Phanerozoic, and have been reported from various lagoons and other environments of post-Ordovician periods. There is a paucity of studies exploring palaeoecology of Ordovician dasycladaleans. Based on examination of 1,089 large thin sections from the Upper Ordovician Lianglitag Formation in 12 drilling wells in the Tarim Basin, Xinjiang, China, dasycladaleans mainly occur in platform margins, less abundant in open platforms, and absent from restricted platform tidal-flats and lagoons. Lagoons used here are in a geological sense, referring to only water bodies enclosed by reefs and banks and featured by abnormal salinity and monotonous eurytopic animals. According to lithology and biota, the lagoons in previous studies are actually open platforms. Thus, this study shows that dasycladaleans are not adapted to lagoons, and this nature of them did not change with time. Statistical analysis shows that occurrence frequency of the Ordovician dasycladaleans is 52% in platform margin environments, 22% in open platform environments, and 0% in restricted platform environments.