High Frequency Cyclic Sequence Of Upper Permian Coal Measures In Panguan Area Of Western Guizhou Province

The thesis fouced on the coal measures of Upper Permian in Panxian,Western Guizhou Province.Seveal theories and methods of sedimentary petrology,sequence stratigraphy,cyclostratigraphy were used to study on the sedimentary environment,sequence stratigraphic framework,Milankovich cycles,genetic mechanism of sequence stratigraphy of Upper Permian coal measures,based on the comprehensive analysis of well logging,biostratigraphic records,core observation,geochemical test results and wavelet analysis.According to environmental analysis,three types of sedimentary facies consisting of carbonate tidal flats,barrier lagoon and shallow water delta,six subfacies and eight microfacies are recognized and their characteristics are summarized as well in Upper Permian coal measures in the study area.By identifying sequence boundary and sequence stratigraphic correlation,Upper Permian coal measures are divided into four third-order sequences.Then the logging data of Upper Permian coal measures in typical drillings were processed by the methods of wavelet analysis and spectrum analysis,the results demonstrated that the sedimentary process of coal measures is obviously affected by astronomical orbital period(long eccentricity,short eccentricity,obliquity and precession).Among the four control factors,the long eccentricity has the strongest effect on the Upper Permian coal measures of Milankovitch cycles.A “floating” astronomical time scale was established by filtering the long and short eccentricity cycles.Finally,taking the long eccentricity cycles as isochronous section and combining with the sedimentary succession and characteristics of cycle boundaries,the Upper Permian coal measures can be further divided into sixteen 4th-order sequences,which helps establish the regional highfrequency cyclic sequence framework of study area and provide geo-chronological constraints on the formation and duration of the synsedimentary volcanic event layers(known as Tonsteins).The patterns and evolutions of palaeogeography and the spatial distribution of coal seams in each cycle were analyzed in the framework of Upper Permian coal measures sequence stratigraphy.The results shows that major coal accumulation occurred in the period of SQ2 and SQ3,and SQ2-1~SQ2-2?SQ3-1~SQ3-2 cycles were determined the advantage coal-containing cycles of Upper Permian coal measures.On this basis,the sedimentary evolutions of SQ2 and SQ3 and coal-accumulating patterns were studied.The results shows that thick-coal-accumulating processes occurs in the middle and upper part of the cycle or the transition period of the base-level,and coal beds deposited in the interdistributary bay of delta front with shallow depth.The controlling factors of sequence stratigraphy were analyzed and were believed to be controlled by the comprehensive impact of global sea level change,tectonic subsidence,sediment supply and climate.Among the four factors,it is considered that the global sea level change during Late Permian was the main controlling factors.Furthermore,the development of high-frequence cycle were interpreted as controlling by Milankovich-astronomical orbital period,driving the cyclical change of climate that lead to the change of glacial sea-level and source supply in the deposition process of high-frequence cycle.