东海扬子浅滩砂质底形研究

A Study of Sandy Bedforms on the Yangtze Shoal in the East China Sea

根据 198 0至 2 0 0 0年间数次专项调查获得的高分辨率地球物理、沉积学等资料 ,并结合水动力环境的分析 ,探讨了东海扬子浅滩砂质底形的成因、形态特征、活动性以及发育的地层年代。研究表明 ,扬子浅滩砂质海底广泛发育沙波地貌 ,按其发育规模可以分为沙波和大型波痕 2类 ,大型波痕按其形态又可分为直线形、弯曲形和格子形 3种。平坦宽阔的地形、丰富的中细砂物源以及较强的潮流和风暴浪流是沙波地貌发育的有利环境条件。柱状岩芯分析和年代测定表明 ,发育沙波地貌的物质的沉积始于冰消期晚期 ,即 10～ 11KaB .P ,全新世中、晚期该区继续接受砂质沉积。扬子浅滩发育的沙波地貌与现今的动力环境相适应 ,仍处于发育和运移状态。

Combining high resolution geophysical and sedimentological data obtained from several special investigations during 1980～2000 with analyses of hydrodynamic environments, this paper studied the cause of formation, pattern, movement and age of stratum of the sandy bedforms on the Yangtze Shoal in the East China Sea. There are two types, megaripples and sand waves, which are widely developed in the Yangtze shoal. The megaripples can be divided into three types, iestraight-crested, branch-crested and chequer-crested megaripples. Flat and wide topography, affluent medium to fine sand and strong tide currents and currents induced by storm waves are the advantageous environmental conditions for the development of megaripples and sand waves. Analyses of coring samples and C 14 dating suggest that the sand layers which could have developed into megaripples and sand waves were deposited after the transgression during 10-11kaB.P. Sandy materials were deposited continually during the middle and late Holocene. It is also suggested that the sandy bedforms are corresponding to the hydrodynamic environments in the area, and are in a developing and movable situation.