Study Of The Genesis And Significance Of Glacial Rocks Of Zhengmuguan Formation Of Sinian System Helanshan In Ningxia

Helanshan of Ningxia is located in the western margin of Ordos Basin, there are a series of special glacigenous rock stratas in Suyukou, Taosigou, Huangqikou, etc., which are covered by slates. Gravels contained in the tillites are characterized as sorting is poor, composition is complex and several shapes exist. And polished surfaces and slicken sides are also found in the tillites. The glacigenous rock stratas in Helanshan belong to Sinian period of Neoproterozoic. Currently, based on the tillites of Helanshan, geologists can research and deduce the activity characteristics of fossil glaciers, sedimentary environment of glaciers, and evolution of paleoclimate, paleogeography and paleostructure. And the tillites are also reference mark of Precambrian stratigraphic correlation between Helanshan and its neighboring regions.Based on the detailed analysis of previous data, photos from geologic reconnaissance, measured sections and petrologic characteristics of gravels, this paper summarizes macro-characteristics of the tillites of Sinian Zhengmuguan formation in Helanshan, Through microscopic identification, this paper summarizes type and composition of the gravels and characteristics of its glacigenous rocks matrixs. In the process of research, the glacigenous rocks matrixs from 14 samples are crumbled into 200 meshes, on which geochemical test of major and trace elements are carried out. And according to the geological data, this research processes test data and carries out geological explanation so as to analyze genesis of this tillites. Then, in comparison with other Sinian glacigenous rock stratas, this paper researches its significance. By researching, this paper finds that this set of tillites lie in transitional zone from sea to land of glacier-coastal shelf when they are forming, which show the oxidation environment of sedimentary. The massive gravels in the lower member of this tillites are formed by the accumulation of rock mass and debris of different size that are transported by glaciers. The morainic conglomeratic sandy-stones in the upper member of this tillites are characterized as banded stripe, laminated structure and dropstones develop, which are formed in the period of glacial recession.