Sedimentary Characteristics and Geneses of Pebbly Meandering River: A Case from Dashihe River in Qinghuangdao~Area

The patterns of sandy meandering river and pebbly braided river had been well documented on their sedimentary characteristics, but the pattern of pebbly meandering river had been rarely previously reported. Based on modern sedimentary investigations on the Xiaobangshuiya-Shangzhuangtuo stretch of Dashihe River in Qinghuangdao Area taken as a typical example of pebbly meandering river, the geomorphology units and sedimentary characteristics are described, and then the depositional succession and model are summarized to insight into its geneses in this paper. The geomorphology units include a single highly-sinuous channel, convex and concave banks alternately locating at the two sides of the channel, launder and small-scale flood plains. Sourced by the nearby mountainous provenance, the sediments are identified as lags deposits, pebbly point-bar deposits, gravelly launder deposits and sandy flood plain deposits with imbricate structure, and large-scale tabular, wedge-shaped and trough cross-bedding from bottom to top, presenting a fining-upward succession called as an atypical dual-structure that is constructed by coarse sediments in the lower and fine sediments in the upper. Accordingly, the pebbly meandering river is featured with geomorphology units similar to a sandy meandering river, and with hydrodynamic conditions, lithologic compositions and depositional succession similar to a pebbly braided river, so are called as dual properties. Integrating with the pebbly meandering river widely occurring in modern mountainous regions, three-graded river terraces in the study area indicated that the river pattern of pebbly meandering river is attributed to regional tectonic uplifts and river’s intense erosional actions. The study in this paper brings a challenge on understanding the classification, distribution and control factors of river patterns. Identifications of geo-historical pebbly meandering rivers should be significant to determine orogenic movements due to their close response to regional tectonic~uplift.