Analysis Of The Development Features And Controlling Factors Of The Strata Deposited In Yanshan Stage In The Area Of Bohai Bay Basin

Bohai Bay Basin is a considerable petroleum province in the eastern part of North China. In recent years, exploration strata has diverted to the deep formation with the advanced of prospecting degree. Bohai Bay Basin had experienced complex geological history and reformation process, development features of strata in different depression and period exist distinction. In addition, predecessors didn't pay much attention to it and the distribution of datum is not uniform. In a word, researches of Yanshanian strata were relatively weak and it affects the prospecting progress.Based on the multitude information of seismic, logging, drilling, palaeontology and regional geology, thesis regard the Bohai Bay Basin as the research object, classify the tectonic sequences of Yanshan era and rock stratigraphic units of each depression and establish the criterion of each formation. On the basis of the stratigraphic classification, this thesis collates the tectonic sequences from three respects such as rock character, palaeophyte feature and remnant stratigraphic distribution, establish the Yanshan era strata framework and analyse the control factors of strata development. Favorable hydrocarbon source rock of Yanshan era in Bohai Bay Basin also is inquired preliminarily.The researches show that the sediments of Yanshan era lower tectonic sequence in Bohai Bay Basin were coal-bearing Clastic sediments. Cyathidites- Quadraeculina- Osmundacidites- Chasmatosporites sporopollen assemblage were found from the lower tectonic sequence which remain confinely and display the character of southern and eastern thicker than northern and western area. The sediments of Yanshan era middle tectonic sequence were mainly fluvial and lacustrine sediments with volcanic rocks. This tectonic sequence distributes widely and thick, a plenty of fossils including a few pollen angiospermarum were found in it. The sediments of Yanshan era upper tectonic sequence were fluvial and shallow lacustyine sediments developing in a period of basin disappearance. This formation was found in few areas and containing lots of pollen angiospermarum.The development of Yanshan era strata were controlled by structure element. Strata's different distribution features range in vertical and horizontal affected by property and intensity of fault activity, type and framework of basin, diversity of volcano and magmation. Climate also affect the lithology and palaeophyte feature: during the early Yanshanian, the climate in Bohai Bay Basin was humid and it turned to be dry and heat in middle-late period. The change of climate lead to the vertical lithology varies from dark mudstone and coal to red coarse clastic rock. Statistical analysis shows that there are two source rocks in Yanshan era lower and middle tectonic sequences in Bohai Bay Basin, western Jizhong Depression, Jiyang Depression and Linqing Depression are Favorable hydrocarbon source rock area worth concern.