Preliminary Study on the Hydrodynamic Mechanism of BeachBar Sandbodies with Environmentally Sensitive Grain Size Components:case study from beachbar sandbody sediments of the upper part of the fourth Member of the Shahejie Formation in the Western Dongying Depression

Key words: 
• beachbar

Abstract: Shoreshallow lacustrine beachbar sandbodies widely developed during the period of the upper submember of the fourth Member of the Shahejie Formation of Paleogene in the Western Dongying Depression. The environmentally sensitive grain size components of beachbar sandbodies have been studied using the method of grain sizestandard deviation according to the description of cores and other correlated analyses and tests. Combined with the analysis of grain size probability curves and the research of palaeotopography and palaeocurrent, there four kinds of environmentally sensitive grain size components were determined in the study area, which respectively represents suspension transportation, coastal current, wave and storm wave or gravity flow. Wave and coastal current are the main hydrodynamics of the four kinds of hydrodynamics which control the formation and development of beachbar sandbodies. Wave is the most important hydrodynamics that control the formation and development of beachbar sandbodies according to the calculation of the percentage of environmentally sensitive grain size components of wave and coastal current in the grain population. The energy of wave and its control degree to the formation and development of beachbar sandbodies decreases from the outer to the inner part of shoreshallow lacustrine. The effects of coastal current mainly exist in the inner part of shoreshallow lacustrine.