舟山群岛册子水道现代潮流沙脊的初步研究

Geopulse甚高分辨率浅地震剖面记录和水深测量结果显示,在舟山群岛册子水道北部东侧发育有一条现代潮流脊,宽度约1~1.2km,研究部分长度超过2km(沙脊两端超出研究海域),脊顶水深50~60m,外翼高20~25m,水深65~85m,内翼高约10m,水深50~70m;脊内层理发育,以向海倾斜为主,表明潮流脊是由岸向海方向堆积发育的。根据地震剖面记录特征和沉积环境,推断潮流脊以细砂和粉砂为主组成,来源于册子水道轴部晚更新世陆相地层的侵蚀物质;由落潮流向东南搬运,再由涨潮流向西北搬运,在潮流脊上沉积而成。潮流脊的发育可能与外钓山岛和舟山本岛在研究海域向西突出有关,造成册子水道显著缩窄、流速加大、底质变粗。

Tidal Current Ridge in the Cezi Channel of the Zhoushan Archipelago,in China

A modern tidal current ridge has been found in the Cezi Channel in the Zhoushan Archipelago, Zhejiang Province, China, by Geopulse very high-resolution shallow seismic profiling and echo sounding surveys. The ridge was found 1 ~ 1.2 km wide and over 2 km long, and both its ends extend out of the study area. The top of the ridge is 50 ~ 60 m deep, while its outer flank is 20 ~ 25 m high and 65 ~ 85m deep, and the inner flank about 10m high and 50 ~ 70m deep. Seismic records show cross-stratification of the ridge, dipping towards sea, which means that the ridge was accumulated from the Wai Diaoshan Island toward the Channel. According to seismic records and the deposition environment, the tidal current ridge is formed with fine sands and silt, from erosion of terrestrial stratum of the Late Pleistocene Age in the Cezi Channel axis. The erosion materials are transported toward southeast by ebb currents, while toward northwest by flood currents and then deposited on the ridge. Development of this tidal current ridge is possibly related to the bulge out of the Wai Diaoshan Is. and the Zhoushan Island, which causes the CeZi Channel outstandingly narrowing, and results in the faster current speed and coarser bottom sediments.