西南地区元古界概论

<正> 我国的元古代地层以蓟县、三峡等剖面为标准,自上而下划分为震旦系、青白口系、蓟县系、长城系和五台系,时限为610—2500百万年。西南地区的元古界自勒克莱(M.A.Leclere,1898)开始研究,已有80多年的研究历史,三十至四十年代通过谭锡畴、李春昱(1929—1933)、王曰伦(1937)、丁道衡(1941)、黄汲清(1945)、孟宪民等(1947)地质前辈的研究,初步查明了本区元古界的基本轮廓。

AN OUTLINE OF PROTEROZOIC ERATHEM IN SOUTHWEST CHINA

The Proterozoic erathem of North China includes the Wutai "system", Changcheng system, Jixian system, Qingbaikou system and Sinian system in an ascending order. It ranges from 2500 m. y. to 600 m. y. in age.The Proterozoic erathem of Southwest China may be divided into four stratigraphical regions, namely, the Yangtze region, the Jiangnan region, the Bayan Har-Qi.nling region and the Xizang-West Yunnan region. Stratigraphically, it consists of 22 groups which can be correlated with the Proterozoic erathem of North China. Among them the Kunyang and Huili groups of the Yangtze region are well exposed.The present paper deals with the sedimentary types and lithological characters of each group and gives an introduction of acritachs and stromatolites of the Kunyang and Huili groups. The major geological events of Proterozoic in Southwest China were three major foldings accompanied with magmtism and metamorphism, i. e. Kangdian movement? (1900m. y. ), Wuling movement(1400 m. y. ) and Jinning movement(800 m. y. ). The last one marked the end of geosynclinal history of the Yangtze region.The activities of oceanic rift (ophiolite suite, 1500 m. y. ), crustal rift (intermediate-basic lava, 1100-1200 m.y.) and continental rift (Early Sinian basic and acidic lavas) probably occurred during the Middle Proterozoic. Stromatolites appeared greatly in the Middle Proterozoic. There was glacial activity in the Early Sinian (700-720 m. y. ) and Metazoans have occurred since the Late Sinian (700 m. y. ).As to the sequence of the Kunyang Group and its correlation with the Huili Group, it is subdivided into the lower Dongchuan subgroup and upper Yimen subgroup, corresponding to the lower and upper subgroups of the Huili Group respectively. The Ailaoshan Group, the Cangshan Group, the Chongshan Group and granulites in Kangding Complex may be correlated with the Lower Proterozoic Wutai "System". The Middle Proterozoic began at 1900 m. y.. The Dahongshan, Hekou, Yanbian and Sibao groups were deposited in the Early Changcheng period. Kunyang, Huili, Xide, Ebian, Huodiya, Bikou and Lancang groups may be equivalent to the Upper Changcheng system-Lower Qingbaikou system. The Baixi and Xiajiang groups correspond to the Qingbaikou system.