厦门湾口外近岸陆架区海底沙波发育特征

利用2014–2017年在台湾海峡西部采集的多波束、单道地震剖面、沉积物粒度样品及海流监测资料,在厦门湾近岸陆架区识别出一系列海底沙波,并对沙波的形态特征、分布规律和沉积物组成特征进行分析,探讨水动力条件及其对沙波发育的影响。结果表明沙波发育区水深一般为10~60 m,地形较平缓开阔,坡度一般为0°~1°;平面上沙波区呈一系列NW-SE向条带状坡地,波脊呈线性或新月形,波脊轴线为SW-NE方向,沙波波长为120~800 m,波高2~12 m,沙波指数较大(>30)。地震剖面显示,波形形态主要分为三类:近对称性沙波、非对称性沙波及叠合沙波。近对称性沙纹的波高较大,沙波指数小;非对称性沙波的波长较长,沙波指数大;稳定沙波经后期水流“改造、激活”形成叠合沙波。砂含量较高,沉积物类型以砂、粉砂质砂及砂质粉砂为主,多为细砂—中砂。厦门湾口外的近岸陆架区水动力较强,流系复杂,总体受浙闽沿岸流、南海表层流和黑潮分支的影响。本区为不正规半日潮,流速为0.3~0.7 m/s,落潮流以S向为主,涨潮流向以NNE向为主,潮流作用对沙波的发育和改造起重要影响。

Sand waves in the shelf area off Xiamen Bay

Based on the multi-beam and single-channel seismic data,sediment grain size distribution data and current data collected from the period of 2014–2017,seafloor sand waves are discovered on the shelf off Xiamen Bay.This paper deals with the morphological features,distribution patterns and sediment composition of the sand waves.Hydrodynamic conditions and their bearing on sand waves are discussed.The results show that the sand waves are mainly developed in the offshore area of 10~60 m in water depth with a slope of 0~1 degree,where the sea bottom is relatively gentle and open.Crests of sand waves show a parallel pattern extending in a NW-SE direction.The axis of the sand wave ridge is SW-NE.Most of the sand waves are 2~12 m high and 0.12~0.8 km long with large sand wave index(>30).In the seismic profiles,there are three types of waves i.e.symmetric sand waves,asymmetric sand waves and superimposed sand waves.The symmetrical sand waves are characterized by larger wave height and smaller wave index,while the asymmetrical sand wave by longer wave length and larger sand wave index.The stable sand wave is a kind of superimposed sand wave reformed and reactivated by the flow in later stage.The offshore shelf of Xiamen Bay and its adjacent waters are rich in sand.The bottom sediments are dominated by silt and fine-medium sand,controlled by hydrological dynamics of the area.Affected by the Zhejiang-Fujian coastal current,the surface current of the South China Sea and the branch of Kuroshio current,the current system of the study area is strong and complicated.With regard to the tidal system,the study area is dominated by irregular semi-diurnal tides with a velocity of 0.3~0.7m/s.Tidal currents play an important role in the development and transformation of sand waves.This paper clarified the distribution pattern,and sediment characteristics of the seafloor sand wave,and provided useful foundation for submarine engineering construction in the study area.