SEDIMENTAL RECORDS AND CHARACTERISTICS OF PALAEOCLIMATE AND PALAEOENVIRONMENT IN THE YANSHAN AREA，NORTH CHINA IN THE MESOPROT EROZOIC AND THE NEOPROTEROZOIC

Abstract

The Proterozoic is one of critical periods Environment of the Earths surface tended to stabilization by degrees in the period Various forms of living beings in the Earth began to occur and develop A lot of studies indicated that the Rodinia supercontinent had been formed in the whole Earth at 1 0～0 8 Ga BP Then North China located in middle or low latitude region connected with Laurentia Platform and Siberia Platform The Mesoproterozoic and the Neoproterozoic in Yanshan area were deposited during the Yanshan-Liaohe Tectonic Cycle (1 8～0 85 Ga BP), and the aulacogen underwent an evolution from initiation through development to consumption in Changchen period, Jixian period and Qinbeikou period respectively The first cover upper the platform crystalline basement was formed mainly by the thick carbonate formation A series of palaeoenvironment variance took place on the Earth in the Proterozoic, such as O 2 level increased and CO 2 level reduced of the atmosphere ocean system, and it began to turn into oxidation from reduction 1 85 Ga BP ago Wide ranging red earth pile occurred with the ceasing of the banded silica-iron formations in the Earths history A large number of steranes, hopanes and isoprenoid were identified from the Precambrian samples Those show that eucaryotes, eubacteria and photoautrophs on the Earth might have appeared in the Palaeoproterozoic time A lot of organisms fossils of early stage of the Earth were found from the Mesoproterozoic Changchen system and Jixian system in Yanshan area They include eucaryotic algae, multicellular algae, coccolith, algal stromatolite, metazoan trace fossil and so on Especially the large-scale unicellular algae and macroscopic multicellular algae fossils found from Changzhougou Formation, Chuanlinggou Formation and Tuanshanzi Formation (1 8～1 6 Ga BP) of Changchen system Those discoveries are of important significance to explore the origin and evolution of different kinds of living things and recover palaeoclimate and palaeoenvironment