Analysis Of Middle Miocene Paleomagnetic Characteristics And Filling Evolution Of Shanwang Basin

Shanwang basin is known as the fossil treasure, but due to the lack of geological time scale study, the deposition period of the Wangwang basin is not clear. The study of the depositional evolution and paleoenvironment of the sedimentary facies has only some simple understanding. We studied the landscape profile and the angle rock formation in the Shanwang basin. On one hand,based on the detailed geological research, the authors first established the age of magnetic strata in Shanwang basin by studying the palaeomagnetic characteristics of Shanwang Formation in Shanwang basin and established an accurate chronological framework. The filling phase constructs the amount of rotation and drift. On the other hand, we analyzed the evolution of basin filling,and divided the sedimentary facies and basin filling evolution stages of the main sedimentary strata in the Shanwang basin. From the elemental geochemical characteristics, we restored the ancient environment of the Shanwang basin. The main conclusions are as follows:(1) The basic geological study confirms that the Shanwang basin is a typical Maar Lake basin. According to the fine paleomagnetism data of diatomite strata in Shanwang Formation and the paleomagnetic polarities of upper and lower strata, the sequence of magnetic polarity of the strata in Shanwang basin was determined. The measured polarity was compared with standard polar column The formation age of the second member of the second member of the Shanwang Formation and the upper third is about 18.524 Ma B.P.?18.056 Ma B.P., and the sedimentation time is slightly less than 0.468 Ma. The diatom shale of the second member of Shanwang Formation is deposited from 18.524 Ma B.P., and the deposition time should be between 0.20 and 0.30 Ma.The sedimentary time of Shanwang Formation in the whole Shanwang Basin is about 18.5 Ma B.P.?17.5 Ma B.P..(2) According to the results of paleomagnetic analysis, the tectonic movement of the Wangwang basin can be divided into three periods: 1.Volcanic eruption period, frequent trough of Tanlu fault zone, deep fault mantle, formation of magma upwelling channel, volcanic eruption, the formation of volcanic basin; 2. Basin stability filling period, the fracture activity is weakened, the depositional environment is relatively stable,the volcanic eruption after the formation of basalts on the base of the formation of Maer Lake, the lake to form a suitable environment for diatoms; 3. The period of extinction, as the rupture activity is active again, the magma is sprayed to cover the Wangwang Basin.(3) It is found that the natural gamma-ray has good response to the continuous natural gamma-ray lithology through the measurement and continuous measurement of the natural gamma-ray. Based on the classification criteria of continental lacustrine and fluvial sedimentary facies, the stratigraphic and stratigraphic strata of horny rock in Shanwang Formation are studied. The first, second, third and fourth member of Shanwang Formation are divided into fluvial facies, lake facies and volcanic overflow facies. According to the old and new sedimentary characteristics of the Shanwang basin, the sedimentary evolution of the basin is divided into four stages: rapid collapse basin stage, fully closed and stable development period, semi-closed silting filling stage and extinction period.(4) The paleoenvironment evolution stage has a good correspondence with the sedimentary facies. The peak of the geochemical indicators in some horizons records the abrupt events of the environment, such as the emergence of tuberculosis layer. The Shanwang basin is divided into four stages: the deep-water and semi-salty lacustrine-semi-shallow saline lakes and the shallow rivers, which are the main sedimentary strata of Shanwang Formation, namely Shanwang Formation. Climate change has a relatively wet and heat into a relatively dry and cold.