华北燕山地区中新元古代沉积记录及其古气候、古环境特征

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

大量研究表明大约 1 0～ 0 8GaBP时期 ,全球形成统一的Rodinia超大陆 ,当时华北地块处于中低纬度地区 ,与劳伦及西伯利亚地块相连。燕山地区的中上元古界是以大套碳酸盐建造为主的结晶基底之上的第一盖层沉积。元古代地球大气—海洋系统发生了O2 增多、CO2 减少的古全球变化 ,1 85GaBP开始由还原性转变为氧化性 ,随着条带状硅铁沉积在全球的终止 ,出现广泛的红土堆积。甾烷、藿烷及类异戊二烯等生物标志物在前寒武纪沉积中的大量检出 ,表明早在古元古代地球上就可能已经有真核生物、真菌及光合细菌存在。近年来燕山中元古界长城系、蓟县系发现大量地球早期生物化石 ,包括真核藻类、多细胞藻类、颗石藻、藻叠层石及后生动物遗迹等 ,对探讨各种生命形式的起源与演化、恢复古环境与古气候变化过程都具有重要的意义。

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