摘要
本文对我国新生代地层中颇具争议的安宁系进行了综合对比分析,确认安宁系位于中新统咸水河底砾岩之上,早更新世初黄河阶地砾石层之下,为中新世中期至上新世沉积。沉积构造、粒度和石英砂表面特征等一致表明,安宁系是与干热气候相应的风砂活动的产物。安宁系及与之同时并存的中国东部风成红土说明,第三纪晚期中国大陆已存在沙漠—风成红土的分异格局。推测第三纪晚期,兰州附近地区处于副热带北侧,西风带南缘,半干旱草原至干旱荒漠草原环境。
On the basis of analysis and correlation of strata in Lanzhou area, it is regarded in this article that the youngest stratum under the Aiming System named by C. C. Young and M.N.Bian in 1936 is a layer of gray-white sandy conglomerate formed in the early Miocene Epoch, basis on the evidences of vertebrate paleontology found at some places such as the north slope of Gaolan Mountain, Hanjinzi, Xianshuihe etc., while the oldest stratum above the Anning System is the sixth terrace gravel layer of Huanghe River (Yellow River) under the Wucheng loess layer at Jiuzhoutai, formed 1.488 ±0.11 Ma (B.P.) dated by the method of gypsum fission trace. Anning System, therefore, was formed in the period of Middle Miocene-Pliocene.
Anning System is fossil eolian sand face of desert in light of many features such as large laminae, sandstone with calcareous cement, sand grainsize compared with desert sand, micro-texture of quartz sand granule including dish-shaped concavity, curved groove, curved edge and silica deposit, etc.
The type of physial environment for the formation, of Anning System may be from semiarid steppe to arid desert steppe, and it mainly formed by the arid climate of Late Tertiary, according to the parameters of environment e.g. redish sand colour, calcareous cemented sandstone, calcareous nodule, and relating to other conclusions of paleogeography and paleoboany.
There must be a paleo-anticyclone centre in the west of Lanzhou controlling whole north China in Late Tertiary according to : (1) the occurence of foreset laminae in Anning System are mainly from west to east; (2) the wide spreading of eolian red earth of Late Tertiary in the east of Lanzhou such as Baode and Jinle formations.
出处
《沉积学报》
CAS
CSCD
北大核心
1990年第4期130-137,共8页
Acta Sedimentologica Sinica
