【摘要】 本文提出海滩反递变纹层自下而上粒度由小到大,重矿物富集于纹层底部,它是前滨冲流“剪切分选”的产物。原生反递变纹层常被激浪破坏和再造,遇到后期加积海滩过程时,才能保存于海滩层理中。海滩层理的现场观测是研究海滩层理反递变纹层形成机理的重要方法之一。更多还原

【Abstract】 The stratifications in a completed beach consist of the seaward-dipping swash cross bedding on the foreshor and the landward-dipping parallel and inclined bedding on the backshore. The reverse graded laminae and wedge-shaped scour structure of the sets are the principle characteri -sties of the swash cross bedding.The grain size increases from the bottom to the top within a reverse graded lamina and heavy minerals are concentrated in the bottom of a lamina. They are the results of the "shear sorting" of swash and backwash in the foreshore swash zone of shallow water with high current speed. The lower current in swash belongs to a grain flow of high velocity, in which the shear sorting is common. So the reverse graded laminae in beach bedding should be quite many. But, due to the fact that the swash has the feature of agitating first and depositing afterwards, and that the swash zone in which the velocity decreases landward is transported, the sedimentary mobile layer of swash within a tidal period is composed of several laminae, mostly four or two. The reverse laminae forming during flood tide generally are disturbed and restructured by surfs and plunge points and the reverse laminae forming during ebb tide may be preserved in the sedimentary mobile layer of swash. Then, they are also disturbed and cut by the swash of the following tidal period and by the storm swash. A small amount of residual primary reverse graded laminae is covered with subsequent additive diposition, forming one reverse graded lamina in beach bedding. Their rate of existence in the beach foreshores in the north of the Shandong Peninsula is only 17 percent of the total beach thickness; while the beaches at back-shore form only normal graded laminae due to the washover and gravity.更多还原