Preliminary Study On Coal Seam Division And Contrast Of Yanan Formation In Jurassic Coalfield In Northern Shaanxi

The Jurassic coalfield in Shaanbei Yuheng-Yushen ore district have simple geological structure and numerous commercial seams with relatively moderate thickness and depth,whose coal resources is also quite abundant.To intensify the division and correlation of strata study and to improve the cognitive level of coal-bearing stratum in this area,have an important strategic role in strengthening the construction of energy and chemical base in Northern Shaanxi and promoting economic development.Based on the results of former related geological studies and the correct understanding of regional geology,firstly,study and contrast on the coal department and the geology and mineral resources department's different division methods of coal bearing strata in this area is introduced,secondly,combined with the geological characteristics and coal quality characteristics of the coal bearing strata,according to the sequence stratigraphy theory,the sedimentary cycle theory,the logging interpretation theory and the seismic interpretation theory,the coal seam division and correlation standards are advanced.Through the division and correlation study,the tectonic features and geological features and division and correlation method of coal-bearing stratum are comparatively cognized.The tectonic of study area is simple,which features overall tectonic shape of monoclinal structure with stratigraphic dip less than 1°,and broad undulating undulations are locally developed.Middle Jurassic Yanan formation is the main coal bearing strata of this area,which is stable and well preserved with thickness from 195.29 m to 255.07 m and average thickness of 223.80 m.Vertically,Yanan formation is mainly characterized by coal-bearing formation consists of multiple sedimentary cycles of fluvial-lacustrine-alluvial plain depositions developed in shore-shallow lacustrine face,which contains sedimentary rock such as gray fine coarse feldspar sandstone,deep gray mudstone,siltstone,black carbon mudstone and coal seam.According to the evolution of the sedimentary system of modern sedimentology and coal accumulation period,and study results of sequence stratigraphy,a scientific and reasonable coal seam numbering scheme is proposed eventually.