Study On The Small Shelly Fossils Of Lower Cambrian In Zhenba County Shaanxi Province

The division of Precambrian and Cambrian boundary was preciously discussed, however the division scheme by lithology or parallel unconformity has been behind the times, and it has been replaced by biostratigraphy. Small Shelly Fossils lie in a special stage, which are the first shell fossils after Ediacaran fauna Late Sinian, these microskeletal fossils suddenly appear as the primary type of fossils at the early stage of Cambrian. It provides the biological evidence for the division of Precambrian and Cambrian boundary. Zhenba county, in the south of Shaanxi province, lies in the middle of Northern Margin of Yangtze Platform, the Sinian and Cambrian stratigraphic successions are well developed and most significant fossil lagerstatten, and therefore, may serve as ideal target for Precambrian-Cambrian high-resolution biostratigraphic research.Three stratigraphical sections are newly measured, more than ten stratigraphical sections are collected, and more than one hundred samples are handled. Bases on the extensive field investigation, laboratory analyses and data collection of distribution and development character of Lower Cambrian in Zhenba County, Shaanxi, The Lower Cambrian is divided according to the lithostratigraphic units, and correlated with the adjacent area. Plenty of Small Shelly Fossils are obtained, which include hyolithelminths, chancelloriids, brachiopod, sponge spicules and some fossils that are not classified. Those fossils are described in the paper, especially the distribution in the longitudinal and transverse direction of stratigraphical section, then biostratigraphic unit are subdivided and correlated in details.In the paper, there are seven genera and thirteen species of hyolithelminths, two genera and three species of chancelloriids, two genera and three species of brachiopod, thirteen species and three new types of sponge spicules, four kind of other fossils. The results broadened the contents of Biozones of Small Shelly Fossils and provide biological evidence for the division of Precambrian and Cambrian boundary.