Characteristics Of Lake Level Change Of Paleogene Dongying Period In Liaodong Bay Area

This paper is based on sedimentary petrology,sequence stratigraphy,paleontology,geophysics and geochemistry and took the stratigraphy of the Paleogene Dongying period in Liaodong Bay area as the object of study.According to the sequence stratigraphic method,Dongying Formation is divided into three sequences,and on this basis,comprehensive used of paleontological methods,geochemical methods,geophysical methods,and stratigraphic methods,the lake level change characteristics of the Paleogene Dongying period in Liaodong Bay area were recovered and the characteristics of the curves recovered by each method were analyzed.Through the paleonta pollen method,the humidity curve was calculated by the relative of sporopollen.Application the dominance diversity of ostracoda,the dominance diversity curve of ostracoda was built by calculated the entropy H(s)of information function.The ratio curve of CaO / MgO,Sr / Cu,Rb / Sr,Mn / Fe and V / Ni were got by using geochemical methods.The palaeo-salinity was recovered by calculating the Sp form boron and combing the ratio curve of Sr/Ba.The trend line of natural gamma was obtained by thinning the natural gamma curve.According to the principle of stratigraphic method,the Fischer diagram is used to obtain the characteristics of relative lake change from the accommodating spatial variation.After analyzing the advantages and disadvantages of the above methods and the applicability in the study area,the curves were compared and analyzed,and on the basis of considering the characteristics of each curve,based on the morphological characteristics of CaO / MgO curves,Mn / Fe curves and Sr / Ba curves,combining the curves of the humidity curve and the dominance diversity curve in the SQd3 sequence and the SQd2 sequence,the curve of the lake in Dongying period is fitted.The sedimentary facies of braided river delta,meandering river delta,fan delta,lake and sublacustrine fan were identified in the study area and the characteristics of the sedimentary facies were analyzed.On the basis of this,the characteristics of sedimentary filling response of lake facies change were discussed based on the characteristics of lake level change.It is considered that the lake surface change has some control effect on the configuration of the sand body,the vertical developmental characteristics of the sedimentary facies and the planar distribution characteristics of the sedimentary body.Based on the analysis of the sequence response characteristics,it is considered that the change of lake level controls the formation of the sequence boundary and the characteristics of the sequence superposition pattern.The sequence boundary in the study area corresponds to the process of descending relative to the lake.Based on the analysis of the sequence superposition pattern,it is considered that the superimposed pattern of the sequence is also affected by the change of lake level,which is caused by the change of lake level and the ratio of A/S,and also analyzed sequence stacking pattern of different structural locations.After further analysis,it is concluded that the forth order sequence,which is mainly affected by climate,can be used to guide the division according to the characteristics of high frequency variation of lake level.