天文地层学研究程序及其在渤海湾盆地东营凹陷的应用实例分析

Research procedure of astrostratigraphy and case study of Dongying Sag,Bohai Bay Basin

天文地层学是基于米兰科维奇旋回理论,研究受地球轨道周期性变化控制形成的沉积地层序列的一门新兴的地层学分支学科。其应用广泛,自问世以来得到了迅速发展,但沉积地层序列替代参数的优选及数据处理方法的运用一直是旋回地层学研究的重点和难点。基于对渤海湾盆地东营凹陷沙河街组三段和四段天文地层旋回划分的研究及对国内外研究成果的调研可知,目前天文地层学研究的沉积地层序列替代参数包括古生物参数、地球物理参数及地球化学参数等;天文旋回识别方法主要有岩性直观识别法和时间序列分析法;轨道周期比值法、天文调谐法和假设检验法是旋回结果检验和调谐的方法。现阶段天文旋回地层研究需要关注的问题主要包括:沉积地层序列替代参数的优选及综合运用、多种时频分析方法的优选、旋回划分结果的校准及天文年代标尺的建立。提出了一套较为系统的从沉积地层序列替代参数选取到时间序列分析方法优选再到旋回结果检验的天文旋回研究流程,为将地层划分精细到千年-万年级别的亚米兰科维奇旋回提供一种可以推广的研究手段和方法,也为其他从事天文旋回的研究者们提供参考和借鉴,共同促进天文地层学的向前发展。

Astrostratigraphy is to study the sedimentary sequence formed by the periodic changes of the Earth's orbit based on the Milankovitch cycle theory.It has been developing rapidly since its inception and is widely applied.However,the application of indicators and methods of data processing have always been the focus and difficulty in cycle stratigraphy research.Based on the division of astronomical cycles in the third and fourth members of Shahejie Formation in the Dongying Sag(Es 3 and Es 4),as well as research results gained from both home and abroad,we know that the alternative parameters of sedimentary stratigraphic sequences in astrostratigraphy research at present include paleontological parameters,geophysical and geochemical parameters,etc.The astronomical cycle identification methods mainly include lithology-based visual identification and time series analysis.While the orbital period ratio method,astronomical modulation method and hypothesis testing method are for checking and tuning the results of cyclotrons.The issues in need of attention in the current astronomical cycle stratigraphic research mainly include:the comprehensive application of alternative indicators of sedimentary stratigraphic sequences,the optimization of multiple time-frequency analysis methods,the calibration of cycle division results,and the establishment of astronomical age scales.In this study,a relatively systematic set of astronomical cycle division schemes is sorted out including the selection of alternative indicators of depositional sequences,the optimization of time series analysis methods,and the verification of cycle results.It will be of value to studying the sub-Milankovitch cycle with fine subdivision of the stratum to the millennium and 10,000-year-old level,and of referential value for researchers interested in astronomical age scales,facilitating the development of astrostratigraphy.