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.