Clay Mineral Composition And Environmental Significance Of Neogene Guantao Formation In Bodong Area

With the in-depth study of Neogene reservoirs in Bodong area,the rapid change of thin sands in horizontal and vertical direction of Guantao Formation has become a difficult point in current exploration.Its genesis is closely related to the change of climatic environment.Finding out the climatic and environmental characteristics of Guantao Formation and its evolution characteristics is the key to solve this problem.As an indicator of environmental change,clay minerals are very sensitive to environmental change.They carry abundant information of environment and climate change in the process of formation and evolution.Therefore,the paleoclimate can be reconstructed through the distribution and combination characteristics of clay minerals and their response to the environment,which provides a basis for the establishment of thin sand depositional system in the next step.The clay minerals of Neogene Guantao Formation in Bodong area are studied in this paper.Based on the X-ray diffraction,scanning electron microscopy,clay mineral content ratio analysis and other index comparison methods,the composition and composition of clay minerals and the indicators were analyzed.The interrelationship explores the environmental significance of the distribution of clay minerals.The study found that:(1)Most of the clay minerals in the study area are debris genes,which are weakly diagenetic,and their characteristics record the environmental information of the source area.The XRD results identified that the clay minerals in the Bodong area mainly include the illite/smectite mixed-layered,kaolinite,chlorite and illite.The average content of illite/smectite mixed-layered is 73.77%;the average content of illite is 6.89%;the average content of kaolinite is 11.73%;the average content of chlorite is 7.61%.Compared with the Minghua Town Group and the Dongying Group,it was found that the Guantao Formation in the Bodong area was dominated by a humid environment.(2)According to the four sequences of Guantao Formation in the target interval,the clay mineral assemblage and relative content in each sequence are studied in this paper:Section SQG4: illite content is generally stable,two ratios increase obviously,kaolinite content increases slightly,chlorite content increases slightly;Section SQG3: clay mineral assemblage,content and ratio are in a relatively stable stage,illite content and ratio are in a relatively stable stage.The content of kaolinite and chlorite increased obviously in the early and later stages,and the content of kaolinite and chlorite was lower;the content of SQG2: illite decreased obviously,the content of kaolinite decreased slightly,and the content of chlorite also decreased obviously;SQG1: clay mineral assemblage and phase change were obvious in the sedimentary period,the relative content of illite was lower,the content of kaolinite fluctuated slightly,and the content of chlorite was stable as a whole,and the content of chlorite was clear.It increases markedly and does not contain montmorillonite.The four sequence segmentsof Guantao Formation are divided into three climatic zones: A(SQG4 + SQG3).The overall climatic characteristics of this stage are warm-semi-humid;B(SQG2).In this stage the climatic characteristics of Bodong region are hot-humid;C(SQG1).In this stage,the climatic characteristics of Bodong region are warm-semi-humid.(3)Based on the longitudinal division of the climatic zone,according to the clay mineral combination on the plane of the study area,the climate environment of each region in the three climatic zones is further analyzed.The results show that the climate of each district under A climate zone is warm-semi-wet in Zone I and Zone II,warmer and semi-humid in Zone III,warm-semi-arid in Zone IV;Climate environment of each district in B climatic zone: the climate of area I,II and III has little difference,which is humid-hot environment,and that of area IV is more hot-humid environment.The climate of each district under C climate: I zone is warm,zone II is hot and humid,zone III and the whole zone have little difference in climate,which is warmer and warmer,and zone IV is warm-semi-arid.