昌黎海岸风成沙丘的形态与沉积构造特征及其成因初探

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

本文论述了昌黎海岸风成沙丘的分布与形成特征、层理构造及其沙丘表面沙波发育情况．并对其成因进行了探讨．沙丘迎风坡表面普遍发育有风成沙纹，层理构造非常发育，有低角度交错层理、大型板状交错层理。海岸沙丘沉积物主要来自滦河．滦河入海泥沙在偏风浪的作用下向北搬运并堆积在海滩上．强劲的向岸风使海滩沙向陆搬运建造成海岸沙丘。目前．沙丘仍在活动之中。

The Changli coastal dunefield, situated on the southwestern shore of Liaodong Bay,is one of the largest coastal dunefields in China. The dune field forms a strip 2-3km wide and more than 30 km long. The dominant dune type in the studied area is transverse dunes, and these dunes have sqpaings of 80-600m with a height 5-38m. Most dune crests are oriented normal to the prevailing wind vector (NE-NEE ).There are close relationships between dune height, width and sapcing (r>0. 8).Eolian sand ripples, composed of well-sorted medium to fine-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 coarselag 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 main trenches, oriented at right angles to the dune crests, two types of stratifications were recongnized. Low-angle cross-strata sets occur on the surfacial parts of the stoss sides, they dip upwind (NE50 -70), with angles less than 11°.High-angle cross-strata sets are the dominant type of stratification in studied area. mostly they are tabular-planar, and measurements show the foreset strata with southwestern dips of 28°- 31°.Sets of cross-strata in the beach are relatively thin and slightly dipping with angles less than 6°.Sand dunes may occur where there is a large supply of sand, a wind to move it, and a place in which it can accumulate. Changli Coast, with wide and low-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 northward and deposited on the beach by the alongshore currents and waves.The onshore wind blows the well-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.