Cyclostratigraphy Research on Well-logging of the Lower Cambrian Qiongzhusi Formation in Southwestern Sichuan Basin
[Objective]The Lower Cambrian in the Sichuan Basin is a key area for understanding the evolution of life and the paleoenvironment,and is a most significant area for future oil and gas exploration.Study of the precise chro-nostratigraphy has both production and scientific value.[Methods]To define the sedimentary sequence in the re-gion,cyclostratigraphical studies were conducted for well Jinye-1.[Results and Conclusions](1)Well-logging re-cords were taken to investigate the effects of content variation in strata components.(2)The K logging series was cho-sen to be the best proxy in the Lower Cambrian Qiongzhusi Formation in the southwestern Sichuan Basin.The K log-ging series was divided into four segments,and spectra for each segment were analyzed in detail.Evolutional spec-trum analysis was conducted for the whole Qiongzhusi Formation.Orbital cycles of 405,131,95,6 and 28 ka were identified in the sedimentary records.A floating astronomical time scale was constructed by applying Gaussian filter-ing of the 405 ka cycle together with the control age of 526.86±0.16 Ma from a related region.(3)The time scale con-tained 29 long-eccentricity cycles,and the optimal sedimentation rate of each logging series segment was found to be 2.5,2.9,3.4 and 4.8 cm/ka.(4)The DYNOT sedimentary noise model and ρ1 were built on the 405 ka tuning time series to obtain the relative sea-level change plots in the time domain.Analysis of relative sea-level change recognized four third-order sequences and four maximum flooding surfaces,and the transgressive-regressive(T-R)cycles.The deposition times of each sequence from early to late are 3.18,2.03,2.97 and 3.63 Ma respectively,with each con-taining 8,5,7 and 9 long eccentricity cycles.(5)The relative sea-level decrease corresponds to the global carbon iso-tope negative excursion;it is presumed that the decreasing sea-level led to oxidation of exposed organic matter,releasing the lighter carbon isotopes and resulting in the negative carbon isotope excursion.
well Jinye-1optimal sedimentation ratefloating astronomical time scalesedimentary noise modelrelative sea-level changes
万方数据
维普
