摘要
中国早中太古代由于火山活动频繁强烈,大气中 CO_2多,受温室效应的影响,古气候具有温暖潮湿的特点。大气不对流,空气中水分不发生地区循环,雨水都降落在沿海及海面上。由于大陆面积小,地形差异不大,尚不致发生内陆干燥气候。内蒙集宁群、冀西北桑干群及太行山阜平群等出现的大理岩,是我国最早的碳酸盐层,一方面反映了海水普遍温暖,同时也反映了海洋中氧己达到了某一临界值和可溶 CO_2浓度较低。集宁群、阜平群中还有我国最早的孔达岩系。下鞍山群残留有少量我国最早的长石砂岩,是温暖潮湿气候的标志。晚太古代时正常的沉积岩较发育,并存在不同的岩相带,例如从冀东到晋南有一条东北向的岩相分界线,此线以东则缺少碳酸盐沉积,以西则含有多层大理岩;面条带状磁铁石英岩则与此相反。这些沉积古地理的特征,似乎反映了古气候的差异,即西部具有广阔而宁静的浅海盆地沉积,具有温暖而潮湿气候的特点,东部则为不稳定岛海火山喷发与间歇沉积的特征,气候不稳定,在火山喷发时气候很高,在间歇沉积时则气温较低。
There was more CO_2 in the early and middle Archaeozoic atmosphere of China because of the frequent and violent volcanic activities.Under the influence of hothouse effect the paleoclimate was characterized by warmth and wetness.Both the convection current of the atmosphere and the local circulation of moisture in the air had not taken place.All of the rainwater fell only on the area along the seashore and on the surface of the sea.Because of the small land and little difference into- pography,the dry climate of inland had not developed.The earliest carbonate.rocks of China are the marbles from the Jining Group,inner Mongolia and the Fuping Group,the Taihangshan Mountains.It shows that the seawater at that time was warm everywhere,and that the oxygen in the sea had reached some critical point and the density of the soluble CO_2 was lower.The earliest khondalites of China occured also in the Jining and Fuping Groups.The Lower Anshan Group contains a few arko- ses which are regarded as the earliest arkoses of China.They are the marks of warm and wet climate. The normal sedimentary rocks were developed quite well in the late Archaeozoic Era and can be divided into some different lithofacies zones For example,there is a lithofacies demarcation line in a northeast-south- west direction from Beijing to the south of shanxi province.To the east of the line,there is short of carbonate sediment,but to the west, there are many layers of marbles.The development of st rippedf erruginous quartzites is contrary to the marbles.These paleogeolraphic features of sediments seem to eflect the difference of the paleoclimate,that is,the west part developed a set of broad and still shallow sea deposit with the characteristics of warm and wet climate;the east part is characterized by unstable eruption of island volcanoes and interval sidements.Moreover. the climate was unsteady:the air temperature was quite high daring the eruptions,lower in the interval periods.
