Abstract

New and generalized published data on the structure, age, and formation stages of deposits of the mantle and alluvial genetic complexes of the first terrace of rivers in the Selenga drainage basin are presented. The sections of the terrace of the Bryanka River in the Bryansk Depression, the Arshan River in the Khilok–Chikoi Depression, and the Shivert-Gol River in the Boro-Gol River basin in Mongolia are described. Information on the terrace structure and on the composition and absolute (radiocarbon) age of deposits is obtained. The first terrace 4–9 (15) m high above low water level is distinguished in the Selenga drainage basin. Large differences in the structure and composition of the terrace deposits depend on the morphology of the river valleys, water discharges, and the structural and tectonic conditions of the river basins. It has been established that the accumulation of sediments of the first river terrace in the Selenga basin began at the end of the Late Pleistocene. The channel, floodplain, and oxbow alluvium facies are distinguished. Channel alluvium was accumulated 30–15 cal kyr BP, and the accumulation of floodplain alluvium occurred during the Late Glacial and Early Holocene (15–8 cal kyr BP). The alluvium is overlain by Holocene sediments of the mantle genetic complex of different composition, genesis, and age reaching 3.5 m in thickness. It has been revealed that the first terrace of rivers in the Selenga drainage basin was formed in the Early Holocene (11.3–8 cal kyr BP) as a result of incising of the rivers during high floods. The chronological stages of sedimentation and soil formation have been identified. There was a long stage of soil formation 7–2 (0) cal kyr BP after the alluvium accumulation stop.

中文翻译：

---

色楞格流域第一级河流阶地的结构、时代及形成阶段

摘要

介绍了色楞格河流域第一级河流阶地地幔沉积物和冲积成因复合体的结构、年龄和形成阶段的新的和广义的已发表数据。描述了蒙古布良斯克凹陷的布良卡河、希洛克-奇科伊凹陷的阿尔尚河和博罗-戈尔河流域的希维特-戈尔河的阶地部分。获得有关阶地结构以及沉积物的成分和绝对（放射性碳）年龄的信息。第一个阶地高出低水位 4-9 (15) 米，在色楞格流域中最为显着。阶地沉积物的结构和成分差异很大，取决于河谷形态、流量以及流域的结构和构造条件。现已确定，色楞格盆地第一河流阶地沉积物的堆积始于晚更新世末期。河道相、漫滩相、牛轭冲积层相均具有明显特征。河道冲积层的堆积时间为30~15卡BP，漫滩冲积层的堆积发生在晚冰期和早全新世（15~8卡BP）。冲积层上覆盖有不同成分、成因和年龄的全新世地幔成因复合体沉积物，厚度达 3.5 m。据透露，色楞格流域的第一个河流阶地形成于全新世早期（11.3-8cal kyr BP），是高洪水期间河流切割的结果。沉积和土壤形成的时间阶段已经确定。冲积层堆积停止后，有一个7-2 (0) cal kyr BP 的长期成土阶段。