摘要： 鄂尔多斯盆地南缘下古生界奥陶系尚未开展旋回地层学分析,识别奥陶系的天文轨道周期信号,以此建立高精度地质年代标尺,并合理划分三级层序,对该区油气勘探具有重要意义。结合旋回地层学理论和信号分解技术,对旬探1井下古生界奥陶系进行了旋回地层学分析。研究结果表明,不同层段的沉积速率存在差异,旬探1井冶里期—亮甲山期沉积速率分布在4.2~5.6 cm/ka之间,马家沟期沉积速率在2.2~5.5 cm/ka之间变化,平凉期—背锅山期沉积速率变大,在4.3~9.3 cm/ka之间变化; 旬探1井奥陶系中存在显著的米兰科维奇旋回信号,记录了偏心率和斜率天文轨道周期,使用405 ka长偏心率周期建立年龄模型,进行天文调谐,以此建立旬探1井奥陶系浮动天文年代标尺,冶里期—亮甲山组沉积时限~3.25 Ma,马家沟组—背锅山组沉积时限~27.4 Ma;结合小波变换,综合分析奥陶系三级层序频率主要分布在0.011 cycles/m左右,并据此将旬探1井奥陶系划分为13个三级层序。本研究为奥陶系层序划分及其天文旋回研究提供了新的定量方法和科学依据,有助于提升地层沉积过程的精细认识和时间尺度的准确性。

关键词: 鄂尔多斯盆地, 奥陶系, 旋回地层学, 天文旋回, 三级层序, 小波变换

Abstract: In the southern margin of the Ordos Basin,no cyclostratigraphic analysis has yet been conducted on the Paleozoic Ordovician to identify astronomical orbital cycle signals. This analysis is crucial for establishing a high-precision geological timescale and reasonably dividing third-order sequences,which is of significant importance for oil and gas exploration in the area. Combining cyclostratigraphic theory and signal decomposition techniques,a cyclostratigraphic analysis of the Paleozoic Ordovician in the Well XT1 was performed. The results indicate that there are differences in sedimentation rates among different strata. The sedimentation rate during the Yeli and Liangjiashan stages in Well XT1 area ranges from 4.2 to 5.6 cm/ka,while the Majiagou stage varies between 2.2 and 5.5 cm/ka. The sedimentation rate during the Pingliang and Beiguoshan stages increases,ranging from 4.3 to 9.3 cm/ka. Significant Milankovitch cycle signals are present in the Ordovician of Well XT1,recording eccentricity and obliquity astronomical orbital periods. A 405 ka eccentricity cycle was used to establish an age model for astronomical tuning,creating a fluctuating astronomical timescale for the Ordovician in Well XT1,with the sedimentation period for the Yeli to Liangjiashan Formations at approximately 3.25 Ma,and for the Majiagou to Beiguoshan Formations at around 27.4 Ma. Using wavelet transformation,the frequency of the Ordovician third-order sequences was primarily distributed around 0.011 cycles/m,allowing the division of the Ordovician in Well XT1 into approximately 13 third-order sequences. This study provides a new quantitative method and scientific basis for the division of Ordovician sequences and the study of astronomical cycles,contributing to a refined understanding of sedimentary processes and the accuracy of timescales.

Key words: Ordos Basin, Ordovician, cyclostratigraphy, astronomical cycles, third-order sequence, wavelet transformation

中图分类号: 

• P534.42