Modern coastal sedimentation in Beihai,Guangxi

The present paper gives a detailed description of geographic zoning,geological agents,sedimentary and ecological characteristics along the modern coasts in Beihai,Guangxi.The types of environments,sediments and organic associations tend to depend on environmental energy.The coastal environments may be subdivided,on the basis of hydrodynamic energy,into six types:(1) high-energy beach;(2) low-energy gulf;(3) medium-energy rocky tidal flat;(4) medium-energy sandy tidal flat;(5) low-energy muddy mangrove tidal flat,and(6) high-energy spratidal dune.The mixed sedimentation of terrigenous quartz and carbonate grains is much developed in high-energy beach and medium-energy rocky and sandy tidal flat environments.At present,intense erosion is developing along the southern coast of the Weizhou Island south of Beihai whereas extensive deposition may be observed along the northern coast.Since the Weizhou Island is rising at a mean velocity of 3.7 cm/yr,the deposition of modern beaches and tidal flats around the Weizhou Island is developed in the environments of relative lowering of sea level.