High Frequency Sequence Stratigraphy Of Late Permian Coal Measures In Liupanshui Area Western Guizhou Constrained By Event Layers

Based on the comprehensive analysis of vertical sedimentary sequence characteristics,geochemical characteristics,biostratigraphic characteristics,spectrum analysis and wavelet analysis of natural gamma ray logging data of more than 10 wells in Liupanshui area,western Guizhou Province,this paper carried out the types and characteristics of sedimentary facies and distribution of marine marker beds of Late Permian coal measures in Liupanshui area In addition,we also studied the distribution of natural gamma high anomaly event layers,recognition and extraction of Michaelis cycle,high-frequency sequence stratigraphy,U-Pb dating of volcanic ash zircon,and evolution of strontium isotope composition.The results of comprehensive analysis of sedimentary environment show that three sedimentary facies types are identified in the upper Permian of Liupanshui area,which are carbonate tidal flat,barrier lagoon and shallow water delta.Combined with trace element sedimentary geochemical test data and logging curve response characteristics,the sedimentary characteristics of each subfacies and microfacies are summarized.Through the identification of sequence boundary,the stable and continuous development of marine marker beds and coal seam correlation in the study area are studied,the third-order sequence is divided,and the internal characteristics of each third-order sequence are summarized.Based on the recognition and extraction of the upper Permian coal measure Milankovitch cycle,the stable Milankovitch cycle information is preserved.The results show that the long period of eccentricity has the strongest response in the stratigraphic cycle.On the basis of the corresponding sequence division results of the long-term cycle,the disturbance of the stratigraphic dip change caused by tectonic activity and the natural gamma high anomaly event layer caused by volcanic activity is eliminated,and the geological model is established The astronomical scale for geological timing of Upper Permian coal measures is established,and 15 middle-term cycles are identified in the upper Permian coal measures,and the high-frequency sequence stratigraphic framework is established.By comparing the horizontal distribution of the natural gamma high anomaly event layer in the sequence stratigraphic framework,there is a widely distributed and very stable natural gamma high anomaly event layer at the bottom of Longtan Formation.The U-Pb isotopic age of zircon is obtained,which is basically consistent with the established astronomical scale.Based on the strontium isotope composition data,combined with the regional and global geological background of Changxing stage,this paper analyzes the response relationship between the strontium isotope evolution trend of Changxing Formation in the study area and the geological events at that time,and attempts to calibrate the strontium isotope age of a layer of limestone near the top of Changxing Formation in the study area.Two types of isotopic dating results verify the rationality and accuracy of the establishment of high frequency sequence stratigraphic framework.