琼州海峡及周边海域沉积环境及近万年以来沉积演化

Sedimentary Environment and Its Evolution of Qiongzhou Strait and Nearby Seas since Last Ten Thousand Years

对琼州海峡及周边海域约600个表层样品进行粒度分析后发现，琼州海峡内沉积物以粗粒的含砾砂及砂为主，白海峡内向口外则由砂向粉砂过渡，最外侧分布有更细粒的粘土质粉砂，东口砂质沉积物边缘以弧形分布为主，西口呈指状分布．按峰态类型可将粒度频率曲线分布划分为海峡东单峰态、海峡东双峰态、海峡内单双峰态、海峡西单峰态及海峡西双峰态5个区域．采用GSTA模型对沉积物运移趋势分析后发现，沉积物在海峡内主要由南北两侧向中间运移，海峡东口沉积物具有比较明显的由口内向口外输运的趋势，海峡西部沉积物出海峡口后显示了向北输运的趋势，沉积物粒度特征分布及运移趋势说明海峡内及两侧三角洲内沉积物主要来自于海峡底部及南北两岸的潮流冲刷物．根据琼州海峡现代沉积环境，结合周边4个柱状沉积物粒度及14^C测年分析，发现琼州海峡的最终形成大约开始在距今8000a前，由于海平面的上升，潮流作用塑造了海峡初期的地貌，直到距今约5000～4600a前，琼州海峡一直处于快速发展阶段，潮流三角洲发育也最广，之后由于暖期的结束，海平面下降，随着潮流作用的减弱，琼州海峡趋于稳定状态，逐渐形成今天的海峡及口外水下三角洲地貌．

About 600 surface sediment samples were collected in the Qiongzhou Strait and the surrounding marine environment, and were analyzed particle-size distribution. Results show that the sediments are dominated by sand and gravel sandsinside the Qiongzhou Strait, and the sediments change gradually from coarser to finer particles, mostly silt and clay sized, away from the inner strait areas to the outside areas. The boundaries of sand sediments spread arched in the east mouth, whereas they spread in the shape of fingers in the west. The distribution of grain size frequency curve can be divided into 5 categories, （a） single kurtosis to the east strait, （b） east strait double kurtosis, （c） single and double kurtosis in the strait, （d） west strait single kurtosis, and （e） west strait double kurtosis. The sediment transport trends was analyzed by the GSTA model, which shows that the sediment mainly moved from the north and south sides to the middle into the strait, whereas in the east area the sediments moved obviously from the strait to the outside sea, and there was a northward trend in the west area. Both the distribution of grain size and the transport trend of the sediments show that the sediments mainly originated from the bottom and side of the strait which were eroded by the tides. Based on interpretation of the modern depositional environment in the Qiongzhou Strait, combined with the grain size characters and the AMS-14^ C data of 4 core samples which were obtained by the gravity corer, it is concluded that the final formation of the Qiongzhou Strait began about 8 000 a ago due to the rise of sea level, and the initial landform was shaped by the tides. In addition, about 5 000 to 4 600 a ago, the Qiongzhou Strait has been in a stage of rapid development, and the tidal deltas spread most widely until the end of the warm period when the sea level dropped and the tide power weakened, which led to the stabilization and formation of the present Qiongzhou Strait.