Distributional Pattern And Controlling Factors Of Beach-Bars

In the lake sedimentary system,the beach-bar reservoirs have received more and more attention.Studying the controlling factors of beach-bar development is of great significance to the distribution law of beach-bar and to guide the exploration and development of oil and gas reservoirs.Now is the key to the past.By analyzing and summarizing the distribution and controlling factors of modern beach-bar deposits,the problem of prediction of the distribution of ancient beach-bar can be solved.The Qinghai Lake is located in the northeastern part of the Qinghai-Tibet Plateau.Beach-bars in the Qinghai Lake are very developed.The structural features and water environment in the Qinghai Lake are similar to those of ancient lake.It is an ideal place to study the distribution and controlling factors of beach-bar.Systematic methods were used in this study,including field investigation,shallow borehole,exploration pit,exploration trench,google earth and indoor analysis.There is obvious heterogeneity in the development of beach-bar in the Qinghai Lake.In general,on the north and the west shore of the Qinghai Lake,beach-bars are less developed,and even the beach-bar is not developed at the lake bay,while the south shore and the east shore beach-bars are very developed and the beach-bars near the Erlangjian and near the Erhai is the most developed.The Qinghai Lake sandy beach-bars are mainly developed in the western section of the south shore of the Qinghai Lake.The sandy gravel beach-bar is mainly developed near Erlangjian.The sandy gravel beach-bar is widely developed throughout the lake area.The gravel beach-bar is mainly developed in the eastern section of the south shore of the Qinghai Lake.The beach-bar can be divided into a beach-bar parallel to the shoreline and a beach-bar oblique to the shoreline.The beach-bars parallel to the coastline are widely developed,while the beach-bars that are oblique to the coastline only develop in the south shore and the east shore of the Qinghai Lake.Since 18,000 years ago,the lake level fluctuation of the Qinghai Lake has been divided into four stages.The lake level elevation has obvious control on the distribution of the beach-bar,and the longer it stays,the more developed the beach-bars.During the fluctuation of the lake level,the beach-bar is easy to form a lagoon on the land side.According to the supply type and development position,the Qinghai Lake beach-bars can be divided into beach-bars developed by open coastal shallow lakes,beach-bars formed by deltas,beach-bars developed by alluvial fans and beach-bars formed by rebuilding bedrock.The source of the beach-bar controls the grain size and composition,and beach-bars is mainly developed between the slope of the terrain between 0.1° and 0.7°.Under the control of the northwest wind,the distribution of beach-bar has obvious zoning characteristics.In the upper wind zone where hydrodynamic is weak,the beach-bar is less developed.In the crosswind area where hydrodynamic is strong,a large number of beach-bar is deposited in the leeward ridges of the topography,and they are developed in beach-bars that are oblique to the shoreline.In the downwind zone where hydrodynamic is the strongest,a large number of beach-bar deposits in the recessed area of the shoreline.Based on the field observations and the theory of coastal dynamics,a comprehensive sedimentary model of beach-bar was established to predict the developmental location and morphology of the beach-bar developed in the lake which is under the prevailing wind control.