旋回分析法在地层剥蚀量估算中的应用——以塔里木盆地玉北地区东部中下奥陶统鹰山组为例

Application of cycle analysis method to estimate the denuded strata thickness:a case study of Middle-Lower Ordovician Yingshan formation of the eastern Yubei area,Tarim basin

针对海相碳酸盐岩地层的沉积及剥蚀特点提出了旋回分析法,并以塔里木盆地玉北地区东部中下奥陶统鹰山组为例,探讨了该方法对剥蚀量计算的精度及有效性.旋回分析法以米兰科维奇旋回理论为依据,选用对古水深变化敏感的钍钾比曲线ln(Th/K)进行频谱分析,筛选出研究区各钻井鹰山组的米兰科维奇旋回,并利用其固有的周期推算出鹰山组的沉积速率.然后根据未经剥蚀井鹰山组残余厚度及沉积速率,确定研究区鹰山组沉积时限.对于经历过剥蚀的钻井,在沉积时限内将残余地层的米氏旋回叠加关系向上延拓,即实现地层被剥蚀厚度值的估算.结果表明:研究区鹰山组残余厚度与剥蚀厚度具有良好的线性相关性,根据鹰山组残余厚度资料即可以反演推算区内鹰山组剥蚀厚度.旋回分析法基础资料来源于测井及地震数据,在纵、横向上均具有较高的分辨率,对塔里木盆地玉北地区东部中下奥陶统鹰山组的应用中具有良好的效果,为研究海相碳酸盐岩地层剥蚀特征提供了新的思路.

According to the sedimentary and denudation characteristics of marine carbonate strata,cycle analysis method was proposed in this paper.The Middle-Lower Ordovician Yingshan formation of Yubei area in Tarim basin,as an example,has been used to prove the accuracy and validity of this method.Cycle analysis method was on the base of Milankovich cycle theory.Thorium potassium ratio curve（In（Th/K））which is sensitive to the water depth was selected to carry out spectral analysis and the Milankovitch cycles in the target strata of everywell were identified.With its inherent period,the deposition rate of Yingshan formation can be calculated.If the wells were free from denudation,the deposition time of Yingshan formation in the study area was determined by its residual thickness and deposition rate.If the wells had suffered from denudation,the denudation thickness value can be obtained by upward continuation of the Milankovitch cycles superimposed relationship of residual strata in the Yingshan formation deposition time.The results show that residual thickness and denudation thickness of Yingshan formation of the study area has a good linear correlation.Consequently,Yingshan formation denudation thickness can be calculated on the basis of its residual thickness data.Because all basic information is derived from logging and seismic data,and with high resolution in both longitudinal and horizontal,this cycle analysis method is applied effectively to the MiddleLower Ordovician Yingshan formation of eastern Yubei area in Tarim basin,which provides a new insight into studying the erosional features of marine carbonate strata.