旋回阶梯底形的动力地貌及其相关沉积物发育特征

The Morphodynamics of Cyclic Steps and Sedimentary Characteristics of Associated Deposits

旋回阶梯(Cyclic Step)是一种与斜坡相关的、向上迁移的、具有周期性水跃特征的底形,广义上还包括了冲槽与冲坑。基于迎流面沉积作用和背流面侵蚀作用的主导程度可将其划分为主沉积型和主侵蚀型两类。旋回阶梯具有长波长的特征,其波高比通常大于10。海(湖)底旋回阶梯的形成与坡度有很大的关系,其坡度范围通常为0.25°~2°,很少超过10°。与该种底形相关的沉积具有不对称透镜状或匙状纵切面形态,主要以块状或递变沉积及后积层发育为主要特征,其中以超临界浊流沉积和大规模向上迁移的沉积物波最为典型。旋回阶梯底形广泛分布于世界上绝大多数沉积环境中,其地貌动力学和相关沉积学研究对于"源—汇"系统、过程—产物具有重要意义。

Cyclic steps are upstream migrating bedforms associated with slopes and cyclic hydraulic jumps broadly including chutes and pools. It can be roughly classified into net depositional or net erosional one according to the predominance of aggradation at the stoss side or erosion at the lee side. Cyclic step is a long wave bedform with the aspect ratio of wavelength to height over 10.Specially, the formation of submarine （sublacustrine） cyclic step is strongly linked with slope gradient. The forming slope gradient usually varies from 0.25°~2°, while less would exceed 10°. Their associated deposits generally show asymmetrical lenticular or spoon shape in the longitudinal section, and they are usually characterized by the occurrence of structureless or coarse tail graded bedding and backset stratification. The supercritical turbidities and large scale, upstream migrating sediment waves are most representative ones. This bedform is widely distributed in most worldwide depositional environments, thus morphdynamics and sedimentological study is very meaningful for source to sink system as well as process and product.