细粒沉积物中不同级次高频层序划分及其地质意义——以东营凹陷沙三下—沙四上亚段泥页岩为例

Division of high-frequency sequences of different orders in fine-grained deposits and its geologic significance:A case study of mud shale from the lower section of the third member to the upper section of the fourth member of Shahejie Formation in Dongying

泥页岩地层中层序划分是目前基础研究中的难点与热点之一。在充分借鉴国外研究成果的基础上,提出了基于多种敏感性指标、依托GR曲线,借助改进后的T-R旋回理论指导,开展泥页岩层段四—五级层序地层划分的方案;同时,提出在连续测试数据支持下,借助天文旋回理论,利用偏心率、斜率、岁差等天文参数,建立泥页岩层段的天文标尺,从而建立六—七级层序单元。在此基础上,借助天文标尺,将渤海湾盆地东营凹陷A井沙四纯上段划分出4个沉积过程,并将各个沉积过程进行定量化计算。利用上述系列方法,将东营凹陷沙三下—沙四上泥岩段划分为8个四级层序,31个五级层序,并通过对沉积过程的定量分析,认为沙四上段第二个准层序组沉积期最有利于生物发育。

The sequence division of mud shale is a focus in basic research.Based on lots of sensitivity parameters,using the natural gamma curves(GR)and the improved TR cycle theory,it was classified in this paper the fourth and fifth orders of sequences in mud shale.Moreover,using continuous testing data,based on the astronomical cycle theory,some parameters such as eccentricity,slope and precession were used to establish an astronomical scale for mud shale in the study area,by which the sixth and seventh orders of sequence units can be identified.Four deposition processes were concluded in the upper section of the fourth member of Shahejie Formation in well A in the Dongying Sag,Bohai Bay Basin,and quantitative calculations were made for each process to estimate the deposition rates in different units.We divided the strata from the lower section of the third member to the upper section of the fourth member of Shahejie Formation into eight fourth order and 31 fifth order units.The quantitative analyses of deposition process showed that the deposition period of the second quasisequence in the upper section of the fourth member of Shahejie Formation was the most conducive to biological development.