南黄海辐射沙洲西太阳沙海域钻孔沉积环境分析

南黄海辐射沙洲枢纽区的西太阳沙海域钻孔岩芯很好地揭示了研究区全新世中晚期潮成沙脊沉积序列和晚更新世末期滨岸潮滩沉积序列。潮成沙脊在垂向上由两个基本的沉积相构成: 出现在-5m水深以上的沙脊-浅潮下相以发育小型沙波交错层理、水平层理、块状层理和缺乏生物扰动为特点; 发育在水深 -5m以下的沙脊-深潮下相以出现脉状层理、波状层理和沙波交错层理组合为特点,具有丰富的生物扰动,并保存有风暴沉积。{14 C}测年数据表明潮成沙脊是中全新世以后形成的,在辐射沙脊群形成之前,研究区经历了晚更新世的滨岸潮滩环境以及早全新世的海侵环境。烂沙洋靠西太阳沙一侧潮流通道目前已切入晚更新世滨岸潮滩相地层,潮道底部约8m厚的淤积层夹有强烈变形的滑塌堆积,可能与台风、风暴潮引起的骤然淤积有关,目前已被{1992~}2003年的海图资料证实。

CORE-RECORDED SEDIMENTARY ENVIRONMENT OF RADIAL TIDAL SAND RIDGE AT JIANGSU OFFSHORE, SOUTH YELLOW SEA, EAST CHINA

There exists a unique radial tidal sand ridge system(RTSRS)which has developed in a convergent-divergent tidal current field between the Changjiang River delta to the south and the abandoned Huanghe River delta to the north. Three cores, with two on the ridge and one on the trough, were drilled in the hinge area between the northern S-N trend tidal sand ridges and the southern W-E trend ones. Two cores on the ridge itself did not drill through the Holocene, whereas the one on the trough has penetrated beneath the Holocene and the Late Pleistocene boundary. Three cores have revealed the Holocene succession of sand ridges and coastal plain succession during the last deglaciation period, which has a good correlation with the Pleistocene glacio-eustatic sea level changes.The sand ridges(revealed by Core RD03A and RD03B)are composed of alternatively two basic units, that is the homogeneous unit and the bioturbated unit. The homogeneous unit is composed of brown-yellowish fine sand and silt fine sand, with minor clay clasts and shell fragments. Small-ripple beddings as well as evenly laminated and massive beddings are common. Bioturbation is very weak to absent. We interpret this unit as shallow sub-tidal environment with water depth less than < -5m. The bioturbated unit is composed of fine sandy silt and silt intercalated with dark grey silt clay. The alternating beddings(flaser bedding and wavy bedding)are commonly present, with minor small-ripple bedding, laminated and massive beddings. The bioturbation in the unit shows a remarked increase. We interpret this unit as deep sub-tidal environment with water depth more than -5m. This unit presents a good preservation of storm-induced sediments, which are composed of shelly sands with shell fragments more than 65 ％ ~70 ％ 。The shelly sediments show a graded bedding and an erosional contacted surface. The Late Pleistocene coastal plain revealed by Core RD03C at depth 8.16~}18.0m below sea floor has a characteristic of intertidal flat. The deglaciation period developed intertidal flat mainly consists of grayish-greenish gray silt fine sand and silt and grey brown fine sand intercalated with clay silt. Thin laminated bedding, small-ripple cross bedding, wavy bedding, and lenticular bedding are common, which indicates a tidal flat genesis. The upper 8.16~}0m loose fine sandy silt intercalated with thin silt clay layers is quite different from the underlying sediments, which represents present channel bottom deposits equivalent to modern sea floor hydrodynamic conditions. The channel deposits show flaser and massive beddings, with occasionally small-ripple beddings. Slump structures with convolute beddings present on the top and middle-lower part, indicating a storm-induced genesis or sediments dragged by strong tide current.The reconstruction shows a coastal plain dominated study area during {13~}12kaB.P. when the sea level was -50~}-70m below present, which is followed by a transgression deposits represented under present coastal plain by tidal-lagoon system. The regressive tidal ridge system downlapped the underlying transgression system during {6~}3kaB.P. , probably reinforced after the Huanghe River debouching into the South Yellow Sea during {1128~}1855A.D.