层序—岩相古地理图及其编制

Case study of sequence-based lithofacies-paleogeography research and mapping of south China

在中国岩相古地理研究历史简要回顾基础上,以层序地层学理论为指导,就如何编制层序—岩相古地理图进行了讨论,首先是编图单元的选择,一是以层序内的体系域为成图单元,二是以相关界面为成图单元。具体方法是在对所研究的层位进行精细的层序地层分析的基础上,进行层序对比,建立等时地层格架。在上述基础上系统编制不同层序内的各体系域或有关界面沉积时的古地理图。以此方法所编制的层序—岩相古地理图具有重要的理论和现实意义,主要表现为更具有等时性、成因连续性和实用性,能更好地反映一个地区在统一地质作用场中的各种地质信息和综合效应;可以揭示出一些新的地质现象,对于覆盖区相带展布及变化具更合理的预测性。进而以中国南方二叠纪为例,在层序划分、对比的基础上,系统编制了一个完整的海平面变化旋回条件下的层序—岩相古地理图,并描述了其平面展布特点。

On the basis of the general review of lithofacies-paleogeography research in China and the sequence stratigraphy, the mapping methodology in relation to the sequence-based lithofacies paleogeography was postulated firstly to involve determining the mapping unit, which included two main procedures. The first one was related to the system tract within the work area and the other to pertinent sequence boundaries. Specific steps comprise building the sequence-stratigraphy framework, based on the fine sequence division and comparison, and then establishing the lithofacies-paleogeography map of separate systems of each sequence. The sequence-based lithofacies-paleogeography map made in this way is marked by several advantages like synchroneity and succession of the sedimentation process and hence is far more practical for exploration purposes. Furthermore, it more precisely reconstructs the primary geologic process, reveals certain unknown facts and proves more informative. The Permian System in South China was eventually exemplified to elaborate the aforementioned mapping method.