嫩江下游现代河流沉积特征

本文运用河流沉积学原理，以黑龙江省富裕县塔哈乡大马岗嫩江现代沉积露头为例，利用探槽，探坑及钻井获取的野外露头资料及室内各种微观分析测试资料，对嫩江下游现代河流沉积特征进行了详细研究，研究表明，该区河流积积自上而下包括了两种河型沉积，底部是以砾石沉积为主的辫状河沉积，其砾石层厚＞5米，横向上可追踪数百米，上部为一低能量曲流河点坝沉积，以中砾质细砂及粉砂沉积为主，底部无明显冲刷面，发育低角度槽状交错层理，同沉积变形层理及波状交错层理，向上过渡为天然堤的粉砂质泥与粉矿薄互层沉积及漫滩粉砂质泥沉积，其整体沉积特征是在一个辫状河泛滥平原上发育起来的低能源曲流河沉积，这一研究为地下复杂的河流相地层识 提供了一个新的实例。

Characteristics of Modern Fluvial Deposits in the Lower Reaches of the Nenjiang River, Northeast China

Using the basic theory of fluvial sedimentology and taking the outcrop of modern deposits of the Nenjiang River at Damagang, Fuyu County, Heilongjiang, as an example, this paper deals with the characteristics of the modern deposits in the lower reaches of the Nenjiang River. It is based on data from outcrop exploratory trenches, pits and drill holes, as well as various microscopic analyses and tests in lab. The study suggests that there be two types of fluvial deposits in this region. The bottom consists of braided river deposits dominated by a more than 5 m thick gravel layer which may be traced laterally as long as a few hundred meters. The top consists of low-energy meandering river point bar deposits dominated by intermediately fine and silty sands. There is no obvious scoured surface on the bottom. Low-angle trough-like cross-bedding, synsedimentary deforma-tional bedding and wavy cross-bedding are well developed in the point bar. Upwards the deposits pass into alternating thin beds of levee silty muds and silts and flood-plain silty muds. As a whole, the sedimentary characteristics of the Damagang deposits are low-energy meandering river deposits developed on the flood plain of a braided river. This study provides a new case for identification of complicated palaeofluvial formation.