基于米兰科维奇高频旋回的地层划分与对比方法——以鄂尔多斯盆地西缘奥陶系重点层系为例

Stratigraphic division and correlation method based on Milankovitch high-frequency cycle——Taking the key Ordovician strata in the western margin of the Ordos Basin as an example

鄂尔多斯盆地奥陶纪构造活动频繁,中央古隆起将鄂尔多斯盆地分隔为盆地西缘和盆地中东部,两侧海域沉积体系和地层系统不同,导致盆地西缘奥陶系重点层系的小层划分困难。为解决此难题,利用米兰科维奇高频旋回对西缘奥陶系重点层系进行地层划分与对比。结果表明,基于米兰科维奇高频旋回识别层序界面的方法,利用自然伽马测井数据求得的累计旋回厚度偏差曲线拐点与三级-四级层序界面具有良好的对应关系,可以建立与鄂尔多斯盆地中东部奥陶系地层对接的、等时的地层格架;并在此基础上,通过分析累计旋回厚度偏差曲线的形态特征,将西缘奥陶系地层旋回划分为“中东部型”、“相对海进型”、“相对海退型”和“倒S型”四种类型。

The Ordovician tectonic activities in the Ordos Basin were frequent,and the Basin was separated into the western and central-eastern parts by the central paleo-uplift.Different sedimentary and stratigraphic systems on both sides of the sea area make it difficult to sub-divide the key layers of the Ordovician in the western edge of the Basin.In order to solve this problem,the Milankovitch high-frequency cycle was used to carry out stratigraphic classification and correlation.The results indicate that the method of identifying sequence boundaries based on Milankovitch high-frequency cycles,using natural gamma logging data,has a good correspondence with the third-fourth order sequence interface,which can establish an isochronous stratigraphic framework connected with the Ordovician strata in the middle and eastern Ordos Basin.On this basis,by analyzing the morphological characteristics of the cumulative cycle thickness deviation curve,the Ordovician stratigraphic cycles in the western margin are divided into four types:"east-central type","relative transgression type","relative regression type",and"inverted S-type".