Analysis Of Sedimentary System In The Lower Cretaceous Riqingwei Basin

The Riqingwei Basin is a newly discovered late Mesozoic NE-trending offshore rift basin in recent years,covering the coastal areas of Rizhao,Qingdao and Weihai in the eastern part of Shandong Province.A set of deep-water gravity flow sedimentary system has been developed in the Lower Cretaceous of the basin,but the relevant sedimentary research is limited to the local area of the basin at present.Therefore,the analysis of sedimentary system of Lower Cretaceous in the Riqingwei Basin has been carried out.on the one hand,provide an in-depth understanding of the comprehensive distribution of the sedimentary facies in this area.On the other hand,since there have been no major oil and gas exploration breakthroughs in adjacent Jiaolai and Huang Hai basins and other continental fault basins,a comprehensive study on sedimentary systems of marine rift basins under the same tectonic setting has been carried out.It has important guiding significance for the exploration of the future oil and gas prospects in this area.Based on detailed observation and sketch of lithology and sedimentary structure characteristics of Zhougezhuang section,Lingshan Island section and Laoshanyakou section in the study area,and combined with 1352m continuous coring observation of Lingshan Island scientific research and drilling well,the type of gravity flow and distribution of sedimentary facies developed in this area are judged.At the same time,the rock types were identified by field sample observation and microscopic thin slice identification,combined with the analysis of heavy minerals in Zhougezhuang area and Lingshan Island area,the source rock types and provenance directions of Lower Cretaceous in the Riqingwei Basin are comprehensively analyzed.The main conclusions drawn from the above analysis are as follows:? The rock types in Zhougezhuang and Lingshan Island area are mainly feldspar lithic sandstone and lithic feldspathic sandstone.? The analysis of heavy minerals in Zhougezhuang area shows that zircons,limonite,garnet and other stable heavy minerals have more contents,which are similar to those in Lingshan Island area,but there are only individual differences.It is indicated that the source rocks in this area are mainly affected by acid magmatic rocks and metamorphic rocks,and that the provenance comes from different directions of the Sulu orogenic belt in combination with the geotectonic position of the area.?Through core observation,it is found that gravity flow deposition and deep-water mud deposit are mainly developed in Lingshan Island area.combination with large-scale deformation structure of soft sediments,a large number ofdebris or mudstone rifts can be seen in sandstone,and a and b member of classical Baoma sequence can be seen in the sandstone.It is indicated that the main gravity flow type are Slumping flow,detrital flow and turbidity flow.The gravity flow type in Zhougezhuang area and Lingshan Island area is different from that in the sandstones where the reverse grain sequence and the normal grain sequence are paired in the hyperpycnal flow deposition,and the softsediment deformation is rare,mainly detrital flow,turbidity flow and hyperpycnal flow deposition;The turbidity flow deposition in the middle part of Laoshan-Yakou area is relatively developed.There are a large number of trench mode,trough mode,heavy load mode and typical Baoma sequence a?b,and the local grain sequence change can be seen in the middle part of Laoshan-Yakou area.?Combined with the comprehensive analysis of lithology,sedimentary sequence and sedimentary structure of Lingshan Island Section,Zhougezhuang Section,Laoshan-Yakou Section and Lingshan Island Scientific drilling well,The sedimentary facies of the Laiyang Group of Lower Cretaceous in the Riqingwei Basin are mainly alluvial fan facies,fan delta facies,submarine fan facies and semi-deep marine facies.The sedimentary facies of Qingshan Group are mainly alluvial fan facies and fan delta facies with multi-layer volcanic facies.