松科1井北孔四方台组—明水组沉积微相及其沉积环境演化

四方台组和明水组是松辽坳陷盆地萎缩阶段的产物。松科1井北孔的连续岩心显示:四方台组发育曲流河亚相和浅湖亚相的沉积,其中以曲流河亚相为主,曲流河亚相发育河床滞留、点砂坝、天然堤、决口扇、决口水道、河漫滩、河漫湖等7种沉积微相,浅湖亚相发育临滨砂坝微相和静水泥质沉积微相;明水组发育曲流河亚相、浅湖亚相和滨湖亚相,明一段以浅湖亚相为主,明二段曲流河、浅湖亚相交替发育。明水组曲流河亚相发育河床滞留、点砂坝、天然堤、决口扇、决口水道、河漫滩、河漫湖等7种微相;浅湖亚相发育浅湖静水泥沉积、临滨砂坝和风暴沉积微相;滨湖亚相发育砂滩和泥滩微相。盆地沉积时期松辽盆地经历了多次湖平面相对升降变化,四方台湖平面最低、明水组二段形成时期湖平面次之、明水组一段形成时期湖平面最高,自下而上形成了一个低—高—低的湖平面变化旋回。沉积物颜色-古气候关系显示四方台组是气温普遍偏高的干旱、半干旱气候;明一段下部是气温偏低的干旱、半干旱环境,上部是气温偏低的干、湿交替环境;明二段气温高低交替变化,下部和中部是干、湿交替环境,上部是干旱、半干旱环境。四方台组—明水组垂向沉积相带的演变是横向上以小型浅水湖泊为沉积中心的沉积体相带向北西方向迁移的结果。

Uppermost Cretaceous sediments: Sedimentary microfacies and sedimentary environment evolution of Sifangtai Formation and Mingshui Formation in SK-Ⅰ(n)

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.