Abstract:

Sifangtai formation and Mingshui formation developed on the uppermost Cretaceous, Songliao sag basin. The continuous rock core of both formations in SKⅠ(n)( the north hole of SK, China continental scientific drilling ) reveals their sedimentary facies and environments. Sifangtai Fm. composed of sediments of meandering river and shallow lake. The sediments of meandering river is an association of some microfacies including channel lag, point bar, natural levee, crevasse splay, crevasse channel, flooded plain and pond. The sediments of shallow lake is another microfacies association including nearshore bar and mudstone of still water. Mingshui Fm. composed of sediments of meandering river, shallow lake and lakeshore. The first member of Mingshui Fm. is dominated by the sediments of shallow lake and the second member is alternation of the sediments of both meandering river and shallow lake. The microfacies of sediments of meandering river in Mingshui Fm. includes channel lag, point bar, natural levee, crevasse splay, crevasse channel, flooded plain and pond, while shallow lake includes mudstone of still water, nearshore bar and tempestite, and lake shore includes sand beach and mud beach. Lake level had undergone variations several times. The lowest lake level occurred in Sifangtai Fm. and the highest lake level in the first member of Mingshui Fm. The lake level change with “lowhighlow” feature shows a cycle from Sifangtai Fm. to Mingshui Fm. The relationship between sediment colors and paleoclimates shows the climate of Sifangtai and Mingshui stages. Sifangtai Fm. presented aridsemiarid with high temperature. The lower part of the first member of Mingshui Fm. presented aridsemiarid with low temperature, and the upper part presented alternation of aridity and humidity with low temperature. The lower and middle part of the second member of Mingshui Fm. presented alternation of aridity and humidity with high temperature and the upper part presented arid and semiarid with high temperature. The vertical change of sedimentary facies from Sifangtai Fm. to Mingshui Fm. shows northwestward migration of sedimentary facies zones whose center was the area of sediments of shallow lake. 

Key words: Key words: Sifangtai Formation; Mingshui Formation; sedimentary microfacies; sedimentary evolution;  Songliao Basin; SKI