频谱分析法在识别米兰科维奇旋回及高频层序中的应用——以塔里木盆地塔中－巴楚地区下奥陶统鹰山组为例

在巴楚地区露头高频层序研究及塔中地区钻测井三级层序划分的基础上，对塔里木盆地塔中地区塔中162井和塔中43井下奥陶统鹰山组层序OSQ2的自然伽马能谱测井ln（Th/K）曲线进行了滤波处理、快速傅里叶变换处理、小波时频分析以及调谐处理，识别出具有米兰科维奇旋回特征的高频旋回。结果表明：斜度（黄赤交角）旋回最为明显，周期为37.0 ka，是以向上变浅为主的六级米级旋回的主要控制因素，其主旋回平均厚度在台地边缘相带的塔中162井及塔中43井中分别为4.55 m及3.97 m，在巴楚地区半局限-开阔台地相带中为2～4 m；95 ka的短偏心率周期是形成五级准层序的主要控制因素，而大致代表四级准层序组形成时限的413 ka长偏心率周期在地层记录中表现并不明显。据高频层序叠置关系分析及平均主旋回个数初步估算，塔中-巴楚地区下奥陶统鹰山组层序OSQ2的形成时限大约为4.92 Ma，塔中43井鹰山组层序OSQ2受后期构造隆升而被剥蚀约192  m。结合四级层序（准层序组）发育时限（413 ka）及其叠置关系,以及与其调谐的小波变换曲线特征，初步将塔中-巴楚地区鹰山组层序OSQ2划分出12个准层序组。自然伽马能谱测井ln（Th/K）曲线包含沉积古水深相对变化的信息，是反映气候变化生成的米兰科维奇旋回层序的良好指标。

Application of Spectral Analysis to Identify Milankovitch Cycles and High-Frequency Sequences-Take The Lower Ordovician Yingshan Formation of Mid-Tarim Basin as An Example

Based on the division in 3th-sequence about loggings and drillings and the study on high-frequency sequence about the outcrops in Bachu area, the authors identifies the high-frequency sequences with the characteristics of Milankovitch cycle, via the filtering, fast Fourier transform, wavelet analysis and tuning processing of the natural gamma spectrometry log ln(Th/K) curves of sequence OSQ2 of Lower Ordovician Yingshan Formation in Tazhong162 and 43 drillings, Tazhong area, Tarim basin. The results show that the most obvious cycle is the obliquity, the period is 37.0 ka, which is the controlling factor of the development of 6th-meter-scale cycle that shallowing upward oriented. The average thickness of the primary cycle is 4.55 m in Tazhong162 drilling and 3.97 m in Tazhong43 drilling in the platform margin facies belt, while 2-4 m in the half-restricted platform-open platform facies belt. The short eccentricity cycle, which period is 95 ka, is the mainly controlling factor in forming the 5th parasequence. The long eccentricity cycle period, 413 ka, which approximately represents the forming time of 4th-parasequence sets, is not obvious in the stratigraphic record. According to the analysis of the high-frequency sequence superimposition and the preliminary estimates about the average number of main cycles, the forming time is approximately 4.92 Ma in the sequence OSQ2 of Lower Ordovician Yingshan Formation in Tazhong-Bachu area. The thickness of the sequence OSQ2 in Yingshan Formation is eroded for about 192 m due to later tectonic uplift. Combined with the forming time(413 ka) of 4th-sequence(parasequence sets) and the superimposition analysis of Milankovitch cycles, and the tuning curves of the wavelet transform, the sequence OSQ2 in Yingshan Formation is preliminarily divided into 12 parasequence sets in Tazhong-Bachu region. The natural gamma ray spectrometry ln(Th/K) curve contains the relative change information in ancient water depth during the deposition period and thus could better reflect the characteristics of Milankovitch cycles caused by the climate change.