甘肃北山地区晚震旦世山岳冰川沉积

Mountain Glacial Deposits of Late Sinian in Beishan Area

甘肃西北和内蒙古西端的北山地区,发育有罗圈冰期和南沱冰期的古冰成岩沉积,在白湖—马鬃山一带构成长达数百公里的山岳冰川隆起带,并分隔了南北两个断陷沉积盆地。其南侧沉积盆地南缘的塔里木古陆当时并没有大陆冰川覆盖,而北侧盆地的北部与洋区相连。冰碛物皆来源于山岳冰川隆起带,常以冰筏形式携带到盆地远处坠落,构成环境多样的含冰碛岩的海相沉积组合。

The present paper discusses the features of mountain glacier sediment of Late Sinian in Beishan area that located in the west end of Inner Mongolia and northwest border of Gansu Province. The mountain glacier uplift belt, as an island-chain in Baihu-Mazongshan region, extends several handreds kilometers, its southern side is fault marine basin in Changheishan-Shuangyingshan-Wutongjing area, and the northern one is slope belt of sea basin, Pochengshan-Heidashan-Xichangjing, joint with the ocean area. The whole area appear'two depressions and one unlift'deposited basin framework. Tarim palacontinent, which located in the southern margin of the basin, was not covered with continental glacier by then. The central island chain uplift belt, consists of Middle Late Proterozoic Qingbaikou System, Jixian System and Changcheng System, was the source region of the palaeo-tillite. The authors found that the Xichangjing profile, as a representive one, is mostly developed. It shows that the Upper Sinian Xichangjing Group contains two sets i.e., the upper and the lower, of the paleoglacigenous rock, between them are the carbonate rock and terrigeneoussclastic sediments, which represent the warm climate condition at interglacial stage. It is suggested that there were two paleoglacial stage developed. In Beishan area, Xichangjing Group of Upper Sinian contacts with the underlying Dahuoluoshan Group, Qingbaikou Systam, and Pingtoushan Group, Jixian System with angular unconformity, and graduauly transited to the overlying Shuangyingshan formation of Cambrian System. The Pochengshan profile clearly indicated that the silicic rock of top of upper palaeo-tillite of Xichangjing Group showed gradual transitional contact with calcarenite containing Eoredlichia sp. fossil pieces, relevantly, the glacial pelitic conglomerate of transition bed from the upper glacigenous rock to Cambrian System contained sponge spicules and micropaleoflora fossils in Xichangjing region, some of which are correspond to that of upper Luoquan formation in Shaanxi and Henan Province. Therefore, it is proved that the upper glacigenous rock of Xichangjing Group belongs to Luoquan Ice Age, the paleoglaoigenous rocks under the interglacial deposits are the products of Nantuo Ice Age. In the area, tills from the mountain glacier were frequently carried away by ice rafting toward both side and droped in the distant places of the basins. As a result, the various environment marine deposit associations that containing tillites were formed.