Investigation Of Phosphatized Microfossils From The Ediacaran Doushantuo Formation Of The Northern Margin Of The Yangtze Plate, Zhenba, South Shaanxi

Diverse of silicified and phosphatized microfossils have been recovered from the Doushantuo Formation of Yangtze Plate, South China. Such fossils from the Weng’an biota are famous for exquisite preservation and great abundance. The Weng’an biota received extend attention since for containing the earliest known embryos of metazoan. Recently, we discovered abundant spherical and tubular phosphatized microfossils from phosphatic rocks in the Ediacaran Doushantuo Formation at Zhenba, southern Shaanxi province, China. The microfossils are all three-dimensionally preserved, and share many similarities with those in Weng’an Biota.Preliminary investigation indicates that spherical microfossils consist of simple spheres and cleavage-like spheres. Their diameters vary from145micrometers to1180micrometers,95percents of them ranging between200-700micrometers. Most spheroids are enveloped in a single smooth vesicle, while a small number of them have multiple layers of vesicles; and ornamented envelops are very rare. They are morphologically similar to Megasphaera in the Weng’an biota,but different from Megasphaera in diameter size, number of vesicle layer and thickness, especially in ratio between simple spheres and cleavage-like spheres (number of simple spheres/number of cheavage-like spheres*100%).Tubular microfossils are variable in outlines cross-sections which are dominated by circular forms. Some of them are enveloped by1-2layers of tubular walls. Although some individuals are similar to Sinocylocyclicus guizhouensis, Quadratitubus orbigoniatus and Crassitubus costatus from the Weng’an biota in general morphology, there still exist remarkable differences in surface and internal structure. The degree of morphologic complexity and diversity of them is slightly higher than tubular microfossils from the Weng’an biota.In term of stratigraphic position, microfossils from Southern Shaanxi were extracted from the top of Doushantuo Formation, while the Weng’an biota comes from middle-upper Doushantuo Formation. In composition, fossils of acanthomorphic acritarchs have so far not been found in the Southern Shaanxi fossil assemblage. Accordingly, we supposed that the microfossil assemblage investigated here is probably slightly younger than the Weng’an biota, representing microfossil community post to extinction of acanthomorphic acritarchs.Nevertheless, microfossils from the uppermost of the Doushantuo Formation in Southern Shaanxi were extracted from phosphatic clasolite. It indicate that clastic rocks rich in silica and clay have great competency in preserving microfossils of soft-bodied organism. So fossil preserving potential of phosphatic clasolite should be paid more attention.