基于米氏旋回理论的高频层序识别与划分——以东海陆架盆地平湖斜坡带宝云亭地区平三段为例

Identification and division of high-frequency sequence based on Milakovitch cycle: A case of the 3rd Member of Pinghu Formation in Baoyunting Area, Pinghu Slope Zone,East China Sea Shelf Basin

地球轨道周期性的变化控制着气候周期性变化,进而对层序叠加样式也会产生重要的影响。东海陆架盆地平湖组沉积时期经历了冷热交替的气候变化,这种气候变化的频繁波动必然会在相应的沉积物中有所记录。利用La(2004)计算方案计算北纬30°、30~40.4Ma期间地球轨道参数变化周期,确定该沉积时期理论米氏旋回周期比值;平湖斜坡带平湖组三段属于海相沉积,构造活动较弱,沉积稳定,物性相近,区域上分布广泛,因此以平湖组三段作为目的层,对该段伽马测井数据进行频谱检测以及一维连续小波变换,分析结果显示不同钻井中平三段沉积地层主要受405ka的长偏心率,131、99ka的短偏心率以及52ka的斜率周期所控制;选择控制平三段地层发育的主要米兰科维奇周期曲线,建立高分辨率天文年代标尺,进而对平三段地层进行高频层序划分,为平湖斜坡带高频层序单元对比框架的建立提供了一种新的有效方法。

Cyclical changes of climate owe its origin to cyclical changes in Earth orbit,which in turn have an effective impact on the pattern of stratigraphic sequence.During the depositional period of the Pinghu Formation,the East China Sea Continental Shelf Basin had suffered from a cold-hot alternating climate,as the records of sedimentation suggest.In this paper,we calculated the time of the variation of earth orbit parameters at the north latitude of 30°,during the time from 30~40.4 Ma using the La(2004)calculation method to determine the theoretical time span of Milakovitch cycles.The 3 rd Member of Pinghu Formation of the Pinghu Slope Belt is the marine sediments characterized by weak tectonic activity,stable sedimentation,similar physical properties and wide coverage.Therefore,it is selected from among others as the target layer to detect the spectrum of gamma data and analyze the one-dimensional continuous wavelet transform.Our results show that the 3 rd Member of Pinghu Formation is dominated by eccentricity cycles of 405 ka、131 ka、99 ka and a slope cycle of 52 ka.A high-resolution astronomical timescale is then established according to the cyclicity of the Milakovitch cycle curve.Upon the basis,the sequence stratigraphy of high-frequency cycle in the 3 rd Member of Pinghu Formation is constructed.Facts prove that the case provides a new effective approach for stratigraphic division and correlation in the Baoyunting area of the Pinghu Slope Zone.