松辽盆地湖泊浅水三角洲沉积动力学研究

ANALYSIS OF THE SEDIMENTARY DYNAMIC PROCESS OF THE SHALLOW-WATER LAKE DELTA IN THE SONGLIAO BASIN, NORTHEAST CHINA

本文在充分利用开发检查井全井段取芯 ,研究沉积微相类型的基础上 ,结合密集开发井网的动态资料 ,分析了各种砂体在井间的连通性与平面上的分布规律 ,系统总结了地形、河流与湖泊大小、气候演化与湖面升降对湖泊浅水三角洲沉积动力学过程及其前缘砂体内部结构。

On the basis of core information from development inspection wells, different types of sedimentary microfacies could be distinguished. And combining hydrodynamic information from the developing well\|nets, the continuity between wells and planar distribution pattern for different sandbodies could be analyzed clearly. It could be possible to systematically summarize the influence of configuration and size of rivers and lakes, climate changes and lake level fluctuation on the sandbodies at the shallow\|water lake delta front and analyze their sedimentary dynamic process.\; During sedimentation of the middle\|upper layers in the Songliao Basin, the basement descended on the whole, the land and subaqueous land relief was very gentle. Due to gentle relief and large lake area, the lake\|level fluctuation could make the coastal line swing largely and quickly. Changes in width of seasonal and periodic coastal line could reach 20\|50 m. the distributary channels in the delta plain stretch into the lakes over long distances due to acceleration and frequent fluctuation of lake level. So the basic conditions for the formation of shallow\|water delta are the very gentle relief and uniform subsidence. The delta plain is connected smoothly with the wide delta front and pre\|delta, without the topset, foreset and bottomset beds, named the three\|fold structure in the Gilbert delta model.\; Under the conditions of gentle basement, large lake area, relatively arid climate and high frequency and amplitude of lake\|level fluctuation, the small and dispersed shallow\|water delta would be destroyed thoroughly by the coastal and swash\|backwash currents and lake\|waves, thus forming coastal deposits.\; As the rivers become strong in energy, the distributary channels in the delta plain would extend over a long distance to the center of the lake, forming characteristic subaqueous distributary channels. During the lake\|level fluctuation, the hydrodynamics of rivers, lake\|waves and coastal currents might transform the distribution pattern of sediments, then induce subaqueous distributary channel sandbodies at the delta from sheetlize to different degrees. If the climate becomes more humid, the lake\|level would be more stable, and seasonal and periodic changes in lake\|level and the hydrodynamics (which reworked the construction and sheetlization of sandbodies) would become weak, too. So, the shallow\|water delta would develop from sheet\|like to lump\|like and branch\|like with respect to its type as the climate becomes humid.\; Under the conditions of gentle basement, small lake area and strong\|energy rivers, the frequency and amplitude of lake\|level fluctuation and the lake hydrodynamics are weaker, while the hydrodynamics and sedimentation of rivers are stronger, favoring the formation of a bird\|foot\|like shallow\|water lake delta.