渤海湾盆地饶阳凹陷早渐新世高精度年代地层格架建立及意义

Establishment and significance of high-resolution Early Oligocene chronostratigraphic framework in Raoyang Sag, Bohai Bay Basin

渤海湾盆地饶阳凹陷"断裂发育"和"多隆多洼"的特点限制了传统测年方法的应用,层序边界绝对地质年代未曾考究。基于旋回地层学和层序地层学理论,选取标准井进行米兰科维奇旋回分析,建立天文年代标尺,计算层序边界绝对地质年龄。以标准井为中心建立等时地层格架,讨论沉积相分布与沉积速率的耦合关系。结果表明:饶阳凹陷沙一段地层沉积时间为2.78 Ma,6个四级气候层序自下而上分别历时320、430、1 000、410、400和220 ka,平均沉积速率约为150 m/Ma,湖盆内不同沉积环境下沉积速率差异显著。旋回地层学和层序地层学的有机结合是陆相湖盆全息地层学研究的必要手段。

Raoyang Sag in Bohai Bay Basin basins features abundant fault systems and several subbasins, which substantially limits the traditional dating methods. Stratigraphic sequences are not granted with geological time controls. We selected a standard well borehole to analyze its Milankovich cycles and to build the astronomical time scale based on cyclostratigraphy and sequence stratigraphy. Then, absolute age controls of sequence boundaries were calculated. Chronostratigraphic frameworks were established with the central standard well, and we discussed the linkage of the facies distribution and sediment accumulation rate. The results show that the first member of the Shahejie in Raoyang Sag underwent a 2.78 Ma deposition. Its six fourth-order went through 320 ka, 430 ka, 1 000 ka, 410 ka, 400 ka and 220 ka, respectively. The sediment accumulation rate is approximately 150 m/Ma on average. Different depositional environments in lake basins possess varied sediment accumulation rate.Furthermore, the integration of cyclostratigraphy and sequence stratigraphy is key tools to the study of the holostratigraphy in continental lake basins.