基于滩坝沉积信息的古风场的定量表征——以渤海湾盆地东营凹陷始新统为例

The paleowind field is not only an important component of climate, as a geological agency, it also controls the sedimentary process. However, paleowind fields are less well studied because ancient winds were ephemeral and often left little trace of their passing. A large amount of beach-bar complexes, which are closely associated with paleowind field during their formation, were preserved in Paleogene shore-shallow lake environments in east China. By taking the Eocene Dongying Depression in Bohai Bay Basin as an example, this study will conduct sedimentology and sequence stratigraphy researches based on core data, well-log data and seismic data. The project proposed here aims to study the lithofacies, hydrodynamic environment, distribution characteristics, to summarize a detailed wind-wave-based classification of large-scale beach-bar complexes. According to: ① thickness of a single bar deposit; ② paleo-water depth of the basin; ③ paleogeomorphy of the basin; ④ paleo-fetch; and ⑤ paleowind direction, this project then tries to explore the method for recovering the paleowind field quantitatively. And after verification by field data, we expect to obtain its evolution curve during the target period, and then discuss its control on the formation of depositional systems along with factors such as provenance, sequence evolution and tectonic framework of the basin. This study will help to improve the study of paleoclimatology, and provide new theory and perspective on interpretation and prediction of depositional systems as well as favourable hydrocarbon reservoirs. Thus, this project has an important scientific and practical significance.

风场不仅是一项重要的气候指标，作为一种地质营力也控制了沉积过程。但由于古大气流场活动遗留下来的有效信息极少，难以据地质记录开展研究。中国东部古近纪滨浅湖环境发育了大量的滩坝砂体，其形成与古风场关系密切。本项目拟以渤海湾盆地东营凹陷始新统为研究对象，综合沉积学、高精度层序地层学，借助岩心、测录井、地震等资料，在对滩坝砂体的岩相、水动力环境、分布规律进行详细研究的基础上，依据风浪过程对该区不同类型的滩坝进行分类。通过对：①单期次滩坝（沙坝）的厚度；②盆地古水深；③盆地古坡度；④古风程；⑤古风向等参数的获取，探索利用滩坝（沙坝）沉积对古风场进行定量恢复的方法，并通过野外资料对其有效性进行鉴定、校正，建立研究区目的层段的古风场演化曲线，探讨风场与物源、层序演化及盆地构造格局等要素耦合对沉积体系的控制。该研究有助于补充古气候学研究，为沉积体系、有利砂体的解释与预测提供新的研究思路与方法，具有重要的理论意义及现实价值。

风场是一项重要的气候指标，不仅反映大气环流信息，作为一种地质营力也控制了沉积过程。但在古气候研究中，有关古风场的研究较少，原因是古大气流场活动遗留下来的有效信息极少，难以从地质记录中加以恢复。中国东部古近系滨浅湖环境发育了大量的滩坝砂体，其形成与古风场关系密切。课题通过研究风浪对滩坝沉积过程的控制，引进古风场的研究；指出滩坝沉积受控于风场-物源-盆地系统（简称“风-源-盆”系统）。主要成果有：.（1）总结了“风-源-盆”系统沉积动力学的研究思路与研究方法。指出古风场及其控制下的古气候控制了沉积体的构造、结构特征；古物源提供了物质基础；古地貌与古水深决定了沉积体的发育位置、范围与规模，三者共同作用决定了沉积体的时空展布；.（2）建立了滩坝的成因模式。依据滨岸带波浪动力特征，将发育在破浪带的沙坝称为远岸坝；发育在碎浪带或内破浪带的沙坝称为近岸坝；发育于冲浪回流带的沙坝称为沿岸坝。发育在波浪遇浅带、波浪重生带、冲浪回流带的沙滩分别称之为外缘滩、坝间滩、沿岸滩，在平面上，滩主要以席状的形式包围于沙坝周围，即“坝间和坝外为滩”；滩坝的形成受控于“风-源-盆”系统的统一作用；.（3）提出了利用古湖泊中滩坝沉积定量恢复古风场的方法。包括：①根据破浪沙坝的走向及横向不对称性恢复古风向；②根据破浪沙坝和沿岸砾质沙坝的厚度定量恢复古风力。该方法为古风场乃至古气候的恢复开辟了新的思路，也为滩坝砂体的形成和预测研究提供了方法。.（4）研究了物源作用与基准面作用对河流-三角洲地层发育的控制作用。对河流的平衡剖面有了新的认识。验证了基准面的下降是河流达到平衡的必要条件之一，并且首次在自然界发现了河流的平衡剖面。