中国大陆架的沉积物分区

SEDIMENT DIVISION IN CHINA CONTINENTAL SHELF

本文试图根据底质类型和水动力环境,并参考沉积物物理、化学、生物特征及堆积地貌等因素,对中国东部及南海北部陆架沉积物进行分区.并将沉积区具体划分九个类型,即:①大河口外泥质沉积区、②沿岸流泥质沉积区、③小环流泥质沉积区、④外陆架泥质沉积区、⑤浪控砂沉积区、⑥潮控砂沉积区、⑦残留砂沉积区、⑧现代混合沉积区、⑨改造混合沉积区.这样更清晰地揭示了底质类型与沉积环境的关系及沉积物分布规律.

Division of the shelf sediments is mainly based on grain size, mineral species, organisms, chemical proptrty and hydrodynamic environments, and also material source and sedimentary geomorphic features should be taken into account. The sediment division in China continental shelf clearly reveals shelf sed-imentation and sediment time-slace distribution law. Surficial sediments in China continental shelf can be divided into 3 kinds acf.ording to arenaceous, pelitic and mixed facies, which can be further subdi-vided into 9 sediment types, disiributed in 45 sedimentary areas. Pelitic sediments have 4 types:(1) Muddy sediments off the mouths of large rivers such as the Huanghe Rirer, old Huanghe River, Changjiang River, Zhu-jiang River and Zhuoshuixi River. Materials brought into sea by these rivers quickly settle down because of sudden hydrodynamic changes.(2) Coastal curr-ent sediments, found in activity areas of coastal currents of southern Liaoning Province, southern Bohai Sea-Huanghai Sea, Zhemin (Zhejiang and Fujian Pro-vinces) and Guangdong Province. These sediments are poorly sorted, with a high content of unstable and flaky minerals and a low one of heavy minerals and organisms. Weak reduction environment. (3) Small circulating current sediments, mainly distributing in the small circulation areas of the northern and southern Huanghai Sea, Hupi Reef and Guangzhou Bay and in the turbulence area of the Haitan Island. In these areas, hydrodynamism is much weaker and sediments have a finer grain size than in the coastal current areas. Organic matter and pyrite are largely concentrated. Reduction environment. (4) Outer shelf pelitic sediments, only seen in Qiongnan (southern Hainan Island) outer shelf. Organic composition increases, but with nothing to do with coastal currents. Arenaceous sediments include 3 types:(5) Wave dominated sandy sediments, found at the end of the Beibu Gulf and in the east of the Leizhou Peninsula, which are high-energy littoral areas with small influence of coastal currents. (6) Tide-dominated sandy sediments, generally forming sedimentary geomorph-ologic system of tidal sand ridges, seen in Liaodong Shoal, western Korean Bay, Subei Shoal, Taiwan Shoal and the exit shpal of the Qiongzhou Strait.(7) Relict sands, belonging to wave or tide-dominated sands at low sea level and distri-buted in the outer shelves, in some straits of the inner shelves, off large river mouths and between bays of the East and South China Seas. The mordern hyd-rodynamic conditions are very favourable for preservation of the sands. Mixed sediments, spreading between the pelitic and the arenaceous, can be divided into two types:(8) Modern mixed sediments. (9) Reworked mixed sediments. The latter exists betweea the modern pelitic sediments and relict sands.