Morphology Sedimentary Structural Characteristics and Genesis of The Changli Coastal Dunes,Hebei Province

The Changli coastal dunefield,situated on the southwestern shore of Liaodong Bay. is one of the largest coastal dunefields in China. The dunefield forms a strip 2一3 km wide and more than 30 km long. The dominant dune type in the studied area is transverse dunes,and these dunes have sqpaings of 80一600m with a height 5-38m. Most dune crests are oriented normal to the prevailing wind vector (NE一NEE)·There are close relationships between dune height,width and sapcing (r>0. 8). Eolian sand ripples,composed of well一sorted medium to fine一grained sand,occur mainly on the stoss sides of dunes,with their long axes parallel to the slope. Granule ripples form in the interdune lows of coarse lag deposits. They are form in the interdune lows of coarse lag deposits. They are usually asymmetrical and large,and move slowly than the sand ripples. In the m ain trenches,oriented at right angles to the dune crests,two types of stratifications were recongnized. Low一angle cross一strata sets occur on the surfacial parts of the stoss sides,they dip upwind (NE50一70),with angles less than 110. High一angle cross一strata sets are the dominant type of stratification in studied area,mostly they are tabular一planar,and measurements show the foreset strata with southwestern dips of 28°一31°. Sets of cross一strata in the beach are relatively thin and slightly dipping with angles less than 60. Sand dunes may occur where there is a协rge supply of sand,a wind to move it,and a place in which it can accumulate. Changli Coast,with wide and low一angle beach,is ideal location for these criteria to be met. The original sand source for the Changli coastal dunes is Luanhe River. The abundant fluvial sediments are transported north ward and deposited on the beach by the alongshore currents and waves. The onshore wind blows the well一sorted sand grains off the beach and transports them landward,then builds up large transverse dunes. At present time,the coastal dunes are still active.