Microflora from the Precambrian-Cambrian boundary strata in the Yangtze Platform
Yin Leiming(Nanjing Institute of Geology and Palaeontology, Academia Sinica, Nanjing, 210008)
The deposited strata within the Precambrian--Camrian transition are well developed and widely distributed in the Yangtze Platform, China. The fossils including microflora,seaweed,vase-like protists, hard part-bearing fauna and "Chengjiang fauna" have been discovered from the Precambrian-Cambrian boundary strata of the Yangtze Platform.Therefore,the Yangtze Platform has become one of the representative areas for studying global events in biosphere, geosphere and atmosphere duriboundary stfata the Precambrian-Cambrian tional period and for determing the Precambrian - Cambrian boundary. The microflora obtained from carbonate, shale, chert and phosphorite of Precambrian-Cambrian boundary strata in the Yangtze Platform are reviewed and qualified in this paper. Two marked microfossil assemblages of Early Cambrian are summarized. One is the Micrhystridium -- Paracymatiosphaera-- Megathrix assemblage from siliceous phosphorites of the lowest Cambrian and the other is Skiagian--Annulum -- Archaeodiscina assemblage from shale in higher level of the lower Cambrian. They are contaporaneous with Anabarites --Circotheca-- Protohertzina small shelly fossil zone and Parabadiella, Eoredlichia trilobite zone respactively. In Yangtze Platform, it is characterized by that a large number of specimens of Micrhystridium complex, including Micrhystridium regulars, M. apliatum, Filisphaeridium echinulatum and F. minutum, commoly are discovered from chens intercalated in carbonate of Early Cambrian.The surprising occurrence of abundant Micrhystridium regulare and some coccoid algae normally indicated the lowest horizon of Cambrian. In comparison with acritarch biostratigraphy of East Europe Platform,it is recognized here that tile oh1Jonostratigraphic distribution of Micrhystridium-Paracymaof Asteridium tornatum-Comaspheridium velvetum biozone in East Europe Platform,and both are probably a little higher than the now favoured boundary level at the appearance of Phycodes pedum in eastern Newfoundland.