基于米兰科维奇周期的沉积速率计算新方法——以东营凹陷牛38井沙三中为例

A new method to calculate sedimentary rates based on Milankovitch Cycles:a case study on middle section of 3rd member of Shahejie Formation in well Niu38,Dongying Sag,Bohai Bay Basin

选择东营凹陷牛38井沙三中地层作为目的层段,对与气候变化紧密相关的自然伽马数据进行频谱分析和连续小波变换,结果显示沙三中地层受对应于旋回厚度12.127 m的短偏心率125 ka周期显著控制。对该周期滤波分析发现,沙三中地层中保存了约40个125 ka周期;并在沙三中底部绝对年龄38.975 Ma的控制下,建立了牛38井沙三中高分辨率天文年代标尺,确定沙三中顶部年龄为33.975 Ma。在区域地层格架的基础上,根据地震、岩心、测井等资料将沙三中东营三角洲精细划分为9期进积体Z1-Z9。对各期进积体进行滑动窗口频谱分析,结果表明沙三中沉积速率随时间先增大后减小,进积体Z4沉积速率达到最大值0.127 m/ka,是三角洲进积最为鼎盛的时期。最后依据沉积速率计算出各期进积体持续时间,推算出了Z1-Z9各界面较为准确的地质年龄。

A case study was carried out in the middle section of the 3rd member of the Shahejie Formation in well Niu38, Dongying Sag, Bohai Bay Basin. Spectrum analysis and continuous wavelet spectrum of GR log which was closely related to climate change indicated that the target interval was significantly controlled by the eccentricity period of 125 ka corresponding to the thickness of 12. 127 m. The filter analysis of this period revealed that about 40 cycles of 125 ka were preserved in the target interval. High-resolution astronomical time scale was established, by means of which the age of the top of the target interval was 33. 975 Ma since that of the bottom of the target interval was 38. 975 Ma. Based on regional stratigraphic framework, combined with seismic, core and logging data, the Dongying delta was divided into 9 periods named Z1-Z9. According to the sliding window spectrum analysis, the sedimentary rates of the target interval first increased and then decreased as time went by. The sedimentary rate of 7_A reached the maximum （0. 127 m/ka） during the most prosperous period of delta prograding. Finally, the duration of each period and more accurate geological age of the interfaces were cal- culated on the basis of sedimentary rates.