陆相层序地层学标准化研究和层序岩相古地理:以四川盆地上三叠统须家河组为例

Research on standardization of continental sequence stratigraphy and palaeogeography:A case study from the Upper Triassic Xujiahe Formation in Sichuan Basin.

层序地层标准化是未来层序地层研究重要发展方向,层序成因模式、标准建立、工业化应用是核心;层序地层学分析的标准工作流程强调识别沉积物成因类型和层序地层界面的原因,向共同方法迈进。针对中国陆相沉积复杂多变的特点,可以利用野外露头伽马仪、元素捕获仪、探地雷达以及元素地球化学等多种手段进行高精度层序划分,识别三级层序界面与洪泛面,建立露头—钻井—地震层序地层格架。可以依据陆相湖盆沉积旋回在古水深、古气候、沉积地球化学特征等方面的定量表征,综合开展高精度层序地层研究。在四川盆地上三叠统须家河组层序-岩相古地理研究中,将须家河组划分为5个三级层序,须家河组二段上、下亚段实际上是2个不同三级层序的基准面上升与下降体系域沉积,须二下段发育进积型三角洲,上段发育退积型三角洲;由于三角洲砂体发育机理明显不同,导致须二下段储层厚度和物性均好于上段,产层主要分布在下段。在层序-岩相古地理研究基础上,进一步明确须二、四、六段是主要储层发育段,层间泥岩也可作为烃源岩。须一、三、五段是主要烃源岩发育段,盆缘规模较小的三角洲砂体也是重要的储层。

Standardization is important for the future research on sequence stratigraphy.The framework includes genetic modeling,establishing standardization and application of industrialization.The workflow emphasizes defining the genetic type of sedimentation and the bounding surfaces.Because of the complexity of continental sedimentation in China,gamma-ray apparatus,element capture device,GPR,element geochemistry and other methods could be used in the research on high-resolution sequence classification,establishment of the sequence stratigraphic framework of outcrop-well-seismic,and identification of third-order bounding surfaces and flooding surfaces.The integrated research on high-resolution sequence stratigraphy depended on quantitative expression of palaeobathymetry,paleoclimate and geochemistry in sedimentary cycles of continental lake basin.Using the technique in the sequence-lithofacies paleographic research of the upper Triassic Xujiahe Formation in Sichuan Basin,the Xujiahe Formation could be divided into five third-order sequences.The second member of Xujiahe Formation was part of different system tracts with rising and falling basal level of two third-order sequences.The lower part of second member was defined as progressive delta and the upper part was regressive.The thickness and physical property of lower part reservoir is better,and pay formation is mainly in lower part,which is due to the different development mechanism of delta sandstones.Based on sequence-paleogeographic research,the second,fourth,and sixth member of the Xujiahe Formation are defined to be the main reservoir,and the interbedded mudstones could be the source rock.The first,third,and fifth member of the Xujiahe Formation are defined to be the main source rocks;the delta sandstone with lesser scale along basin margin is a significant reservoir too.