Miaolingian (Cambrian)–Early Ordovician Acritarchs from Baishan Area, Jilin Province, China: Stratigraphical Significance

The Cambrian Explosion and the Great Ordovician Biodiversification Event (GOBE) may be considered as parts of a single, long-term early Palaeozoic radiation. The two events are possibly only artificially separated because relatively few palaeontologial investigations are available from the ‘Furongian gap’, a poorly understood interval between the well-studied lower Cambrian and Ordovician intervals. The “plankton revolution”, initiated during the Furongian (Cambrian) and Early Ordovician, preceded the dominance of “level-bottom” and “reef communities” that evolved later in the Ordovician. As major contributors to the primary productivity, the acritarchs—representative of phytoplanktonic groups—played a critical role in the construction and evolution of epipelagic ecosystems. Therefore, the paleontological, palaeoecological and biostratigraphical studies of the acritarchs, in particular spanning the Miaolingian (Cambrian) to Early Ordovician, are of great significance for understanding the biotic macroevolution throughout the Early Palaeozoic, because his transitional interval provides an optimal window to exploring faunal replacements, ecosystem change, and the relationship between the two Cambrian and Ordovician radiations. In the present study, two classic sections, the Xiaoyangqiao and Muxiantougou sections, spanning the Miaolingian (Cambrian) to Tremadocian (Ordovician), in the Baishan area, Jilin Province, China, were systematically sampled for acritarchs and associated organisms. A total of 188 samples from these two sections were processed. Thirty-eight species of 22 acritarch genera are recognized, 12 species of which are reported for the first time from the Baishan area. The assemblages are dominated by Leiosphaeridia, Polygonium, Pterospermopsis, Timofeevia, Synsphaeridium and Priscogalea in the Xiaoyangqiao section, whereas the genera Leiosphaeridia, Polygonium, Timofeevia, Synsphaeridium, Priscogalea, Pterospermopsis, and Baltisphaeridium are the most abundant in the Muxiantougou section. Besides acritarchs, several morphologic types of Small Carbonaceous Fossils (SCFs) were also discovered in these two sections. Several acritarch display a stratigraphical importance from the Miaolingian to Tremadocian. Ninadiacrodiumis considered to be an index taxon to define the middle and late Furongian. It appears from the middle Fengshan Formation (Proconodontus Biozone) to the uppermost Furongian in the Xiaoyangqiao section, allowing international correlation. Another stratigraphically importance genus is Athabascaella, whose FAD has the potential to define the Cambrian–Ordovician boundary, by establishing the stratigraphic sequence of its species in ascending order: Athabascaellarossii, Athabascaellapenika and Athabascaellaplayfordii. Furthermore, the distribution trend of “Dominant Group Assemblage of Acritarchs”, is proposed to be used for biostratigraphical correlation within the basin. This approach is exemplified by the recognition of the Polygonium-TimofeeviaAssemblage within the conodont Cordylodusproavus Biozone in the Baishan area.