第四纪昌平冲积扇沉积特征研究

摘要

In view of the alluvial fan depositional model of the insufficient of the research,proposed the alluvial fan sedimentary characteristics.The deposition model of the Changping alluvial fan is proposed based regional and outcrop geology.In doing so, lithofacies and hierarchy interface analysis approach,in combination with the theory of sedimentology and reservoir architecture, has been applied.The result shows that the outcrop of alluvial fan can be catigoried into five types of lithofacies,which can be grouped into three key architecture elements.In the downstream direction,alluvial fan develops sheet-flood,braided stream and runoff sedimentary bodies successively.However,braided stream deposits constitute the main body of the alluvial fan.After sur-ging out of the mountain pass,the water currents stack strongly in leaf shape,then gradually disperse and branch into multiple braided river channels relatively stable in a certain period,and finally scatter into more unstable runoffs.After multi-stages of floods,braided channels shift and stack at different positions,joining into a big piece of fan-shaped sandy conglomerate complex.%针对不完善的冲积扇沉积模式，通过研究提出了第四纪昌平冲积扇沉积构型要素和沉积模式。在野外露头及区域背景资料的条件下，利用岩石相与层次界面分析的方法，结合沉积学及储层理论，建立了第四纪昌平冲积扇沉积模式。结果表明：露头区可以识别5类典型的岩石相类型，组合成3类关键构型要素。以此为基础，提出了冲积扇顺流方向依次发育成片流、辫流和径流3类砂砾岩体，其中以辫流水道为主体沉积单元。在洪水涌出山口后，水流强烈片状堆积，然后逐渐分散形成一段时期内相对稳定的多条辫流水道，最后，水流进一步发散，形成更多条不稳定的径流水道。多期次的山洪暴发后，辫流水道在不同位置迁移交错叠置，形成了平面连片状扇形砂砾岩体。