【Objective】The Lower Carboniferous Dawuba Formation in southwest Guizhou has developed a set of shale with great exploration potential. However, the scheme of sequence stratigraphic division is not unitive and the understanding of sequence development mechanism is unclear, which restricts the promotion of unconventional oil and gas exploration. Therefore, this paper carries out cyclostratigraphic analysis and sequence stratigraphy research on this set of shale stratum, aiming to realize the "quantitative" stratigraphic division of shale from the perspective of orbital cycles.【Methods】The Well QSD-1 (1457-2466 m) was selected as the research object, and the gamma ray logging curve was used as the proxy index, the cyclostratigraphic analysis and sequence stratigraphy were carried out by using time series analysis, INPEFA analysis and wavelet analysis.【Results】Obvious orbital cycles have been recognized of the Lower Carboniferous Dawuba Formation shales in Southwest Guizhou. The optimal sedimentation rate of the stratum was estimated by COCO is 16.4 cm/ka, and the matching sedimentation thickness of 66.42 m represents the long eccentricity cycle of 405 ka. Spectral analysis was conducted again for GR series (1457-1932 m and 1932-2466 m) of Well QSD-1, and the optimal sedimentation rate was estimated to be 16.5 cm/ka in the upper section and 11.2 cm/ka in the lower section. The filtering results show that 19 long eccentricity cycles are recorded in Dawuba Formation. The "floating" astronomical time scale of Dawuba Formation is established, and the duration of Dawuba Formation is estimated to be about 7.86Ma. The relative sea level change curve of Dawuba Formation is restored by establishing the sedimentary noise model (DYNOT and ρ1) of the research interval. Based on the age framework established by the cyclostratigraphic research, according to the extreme value of the relative sea level change curve, combined with the results of INPEFA analysis and wavelet analysis, the third-level sequence boundary and the maximum flooding surface of Well QSD-1 were recognized. Six third-order sequence boundaries and five third-order sequences were recognized in Well QSD-1 Dawuba Formation, and the development of third-order sequences were correlated by obliquity amplitude modulation (AM) cycle (~1.2 Ma). 【Conclusion】The research method of cyclostratigraphy is applied to the stratigraphic division of Lower Carboniferous Dawuba Formation shale in southwest Guizhou, and the relationship between astronomical orbit parameters and relative sea level changes at different time scales is discussed, and the third and fourth order stratigraphy are divided. Cyclostratigraphic provides the possibility for the correlation of marine shales on the ten thousand years time scale, provides a fine age framework for the prediction of high-quality source rock development intervals in shale oil and gas exploration, and provides theoretical guidance for oil and gas exploration in shale.
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