The Coal Accumulation Patterns Of Pinghu Formation In Pingbei Area, Xihu Depression

The thesis focused on the coal-bearing strata of Pinghu Formation in Pingbei area, Xihudepression. Several theories and methods sedimentary, sedimentary of petrology, sequencestratigraphy, sedimentary geochemistry and coal geology were used to interpret therelationship between stratigraphy cycles and coal formation in the study area. Based on themore than20drilling practical measurable results, two sedimentary facies,delta, barrierdams-lagoon, and the characteristics of each sedimentary facies were summarized. Accordingto determination maceral of coal-coring and analysis of coal accumulation, the results showsthat, coal are grey-black half bright–half dark coal briquetee, organic micro-constituentmajors in vitrinoid group. the main places of coal formation are delta environment. Coal wasformed in the moist lower delta plain and delta front low moor, which influence by pulseseawater strongy, and it’s performance of sulfur content in coal is high.Based on the cores, well logging, seismic emission characteristics, geochemical andexisting research data, according to principle of division of sedimentary based waveletanalysis, three long time base level cycle, twelve middle time base level cycle and forty eightshort time base level cycle framework was established. Combined with regional tectonicevolution, the evolution of paleogeography of Pinghu Formation is studied and thedepositional model were established.According to the mathematical statistics method, based the division of sedimentary cyclesand interpretation of coal, IIB and IIC cycles were determined the advantage coal-containingcycles of Pinghu Formtion. On this basis, the sedimentary evolution of IIB and IIC and coalaccumulation is studied. The results shows (for example IIC cycle), the development of deltain IIC had experienced the early construction, middle waste, and late development in the studyarea. Coal beds deposited in the a peat sweap occurred in the delta plain and the delta front,and the waste period when delta progradation converse to retrogradation, is the best time toaccumulate coal beds.The coal measures of Pinghu Formation are well developed in this area, is controlled bypaleostructure and paleogeography, and related to the relative sea level. And thesynsedimentary fault was the primary control effect. The gentle slope parallel, broom, steepslope fault terrace are divided in syndepositional structural slope break zone in this area, the differentslope break belt and their combination lead to different coal-forming patterm and coal bearing property,and is the main reason causing the difference of coalbed distribution of the study area. Morover, Theactivity of syndepositional faults also control the accommodating space of downthrow in a certain degree,and further controlled distribution of Pinghu formation and the coal measures depositon.Simultaneously, the changes in the relative sea level also determined the distributionof sedimentary envirment in space and plane, to control the development location of coalsource rocks and its preservation condition.