乌南次凹南屯组高精度层序划分及地质意义

High Precision Sequence Division and Geological Significance of Nantun Formation in Wunan Subsag

依据岩芯、录井和测井等方面资料,对海拉尔盆地乌尔逊凹陷乌南次凹南屯组内的高精度层序地层格架及其控制下的沉积体系展布特征进行了研究。结果表明,研究区南屯组主要发育有5类层序界面,共划分出3个三级层序和9个四级层序。纵观各层序的残留地层厚度变化,可发现在南屯组沉积时期沉降中心逐渐西移,地层展布特征自下至上由“中厚-东、西薄”逐渐过渡为“西厚-东薄”的变化规律。乌南次凹南屯组沉积时期主要发育有辫状河三角洲、扇三角洲、湖底扇及湖泊4种沉积体系,沉积体系平面展布具有“东西分带”的特点,其中扇三角洲沉积体系主要发育在西部乌西陡坡带,辫状河三角洲沉积体系主要发育在东部乌东缓坡带,不同时期各沉积体系的平面展布特征具有明显的继承性。

Based on core, logging and logging data, the high-precision sequence stratigraphic framework in Nantun formation of Wunan subsag, Wuerxun depression, Hailar basin and the distribution characteristics of sedimentary systems under its control are studied. The results show that there are five types of sequence boundaries in Nantun formation, which can be divided into three third‐order sequences and nine fourth-order sequences. Throughout the variation of residual stratum thickness of each sequence, it can be found that the sedimentation center of Nantun formation moved westward gradually, and the stratum distribution characteristics changed from "moderate thickness to east and west thin" to "west thick to east thin" gradually from bottom to top. During the sedimentary period of Nantun formation in Wunan subsag, four sedimentary systems were developed, including braided river delta, fan delta, sublacustrine fan and lake. Each sedimentary system has the characteristics of "east-west zoning". The fan delta sedimentary system mainly develops in the western Wuxi steep slope zone, and the braided river delta sedimentary system mainly develops in the eastern Wudong gentle slope zone. The distribution characteristics of sedimentary system in different periods have obvious inheritance.