Abstract: One of the key issues in shale oil and gas exploration is to establish a high-precision sequence stratigraphy to accurately predict sweet spots.The relative lithological continuousness and subtle character varations of shale sediments have made it difficult to define key boundaries between sequences.This paper,based on a comprehensive investigation of case studies of shale reservoirs both in the North America and China,suggests that occurrences such as relatively shallow water facies,small scour surface,low-angle shale beds truncation,deformed soft sediments,shelly laminae and thrust clastics in shale,can be viewed as important sedimentary markers of sequence boundaries.For formations without the above-mentioned markers but of the same geological timing,the paper suggests that to recognize the sequence boundaries or the maximum flooding surface,the following proxies and methods should be applied:geochemical indexes such as redox conditions (e.g.organic geochemical parameters,inorganic trace/dominant element ratios) and organic matter/mineral accumulation patterns (e.g.organic matter content,sediment density,and mineral content),combined with observations of lithology facies interfaces,different types of lag deposits,pyrite ooids and phosphate nodules.The paper summaries the commonly acknowledged sedimentary features and geochemical indexes for sequence stratigraphy division with the help of well-logging data analyses,and proposes that,by using well-logging data,lithofacies combinations,sedimentary features and geochemical parameters,it is workable to divide third-order sequences and establish higher order of sequence stratigraphy.

Key words: erosion surface, sedimentary feature, geochemistry, sequence stratigraphy, marine shale