The Sedimentary Characteristics And Evolution Of Shell Ridge, North Coast Of Shandong Province

The shell ridge II on north coast of Shandong province is the epitome of the whole shell ridge on west and south coast of the Bohai Bay, which is characteristic of typicality and integrality. The shell ridge II on north coast of Shandong province is taken as the object on the background of the south and west coast of the Bohai Bay. The aim of this thesis is to analyze the sedimentary character and subfacies, interpret the formation mechanism and further to discuss the evolution of shell ridge.It has been found by field investigation that there have two raw shell ridges in study area, respectively as shell ridgeIVand shell ridge II .Shell ridgelV has been buried while shell ridge II is growing. A large number of 14C data prove that there is a difference of ages in the same shell ridge though they apparently distribute with the same trend, which suggests that shell ridge is formed periodically and alternate with deltaic progradation. Bivalve and gastropoda are the main species building up the shell ridge, of which the content of shell is more than 95%. This is rarely compared with other shell riges in the world.The data from trench and core disclose the sedimentary characteristic and evolutional process. Shell ridge subfacies is formed by storm and composed of shell and shell fragments; shell ridge infilled subfacies is formed by wind and composed of shell debris and shell sand. The two subfacies alternately sediment and form the particular beddings.Supply of shell material, change of tidal flat's profile, storm, wind and the shift of Yellow River's route are the main factors affecting the development of shell ridge. While the Yellow River changes its route, the shoreline is eroded along the abandoned delta coast. During process of tidal flat developing toward the balance, the amount of shell is largely increased. Storm winnows the shell and it's fragments from tidal flat, carries them toward land and deposits on the average high water line. Later, under the weathering and sorting of wind, shell ridge is rebuilt and heightened. This thesisestablished the relationship of the critical velocity and grain size of shell sand by the test of specific gravity and Wind Tunnel Test. Apart from the factor of specific gravity factor, the flatter shape takes an important part in the critical velocity. On the basis of above analysis, the evolution process of shell ridge has been discussed further, and provides the theoretical proof for studying the ancient environment.