中国现代网状河流沉积特征和沉积模式

中国境内的许多河流发育有网状河段,从长江、黑龙江、珠江等这样的大型河流到嫩江、赣江等中小型河流都有。依据这些网状河的地理和构造背景的不同,可以把它们划分为:平原网状河流、山谷网状河流、入湖三角洲平原网状河流和入海三角洲平原网状河流四大类型。作者通过实地挖掘探槽、密集采样,对嫩江齐齐哈尔平原网状河段、赣江入湖三角洲平原网状河段、珠江入海三角洲平原网状河段沉积特征进行了详细描述和研究,并建立了网状河的沉积模式,探讨了网状河的成因。认为网状河流体系的发育不受气候和地理位置的限制,低坡降是形成网状河的必要条件,相对稳定的网状河道不同于曲流河和辫状河,湿地环境是网状河流体系中最发育的地貌单元,堤岸植被繁茂、粘结性高是河道稳定的重要因素,与曲流河和辫状河相比,网状河出现的几率较低。

Depositional Characterisytics and Models of the Modern Anastomosing River in China

The anastomosing fluvial system was considered as the same term of the braided fluvial system, but the anastomsing stream is distinct from the well-known meandering and braided river. Smith described the anastomosing fluvial system as "a low energy complex of several interconnected channels of variable sinuosity crossing a wetland and forming many elongate islands." Many Chinese rivers have anastomosing reaches, including some large rivers such as Changjiang River, Heilongjiang River, Zhujiang River and some middle-small rivers as Neijiang and Ganjiang River. Based on their physical geography and structural background, they can be divided into four types: plain anastomosing river, vale anastomosing river, lacustrine deltaic plain anastomosing river, marine deltaic plain anastomosing river. Three anastomosed river systems are described. They are anastomosing river in Qiqihaer section of Neijiang River, Ganjiang deltaplain anastomosing river and Zhujiang deltaplain anastomosing river. These rivers contain low gradient, high aggradation rates, multiple channel and large-area wetland between the channels. Channels, natural levees, crevasse-splay, floodplain, lakes, marshes and eolian dunes are important morphological and sedimentary units. Anastomosing channel-filling sediments are mainly composed of pebbly sand and medium to fine sands. Internally channel sandbody consist mainly of trough cross-bedding and oblique bedding. The other morphological units are mainly composed of fine-grained sediments. Some basic characteristics are as follows: climate and geography are not controlling factors of anastomosis; Low gradient is an essential condition for developing anastomosed river systems; Stable multiple channels are different from meandering and braided river; Wetland is major sedimentary unit; Primary factor of channel stabality is dense vegetation on the nature levees and high cohesiveness; Modern examples of anastomosed river systems are not common