Chemical Composition of Bottom Sediments of the Zeya and Selemdzha Rivers as a Reflection of Drainage Area Weathering

This paper reports the results of chemical study of bottom sediments of the Zeya and Selemdzha rivers, the largest water streams of the Amur River basin. It was established that the bottom sediments are depleted in practically all analyzed major and trace elements as compared to the upper continental crust (UCC) and Post-Archean Australian Shale (PAAS). It is shown that the bottom sediments of the studied rivers are chemically close to those of the Northeastern China rivers, which is related to the similar geographical and climatic environments. Examination of major-component proportions and trace-element variations suggests that the bottom sediments of the middle reaches of the Zeya River were formed from chemically reworked sources. In contrast, the bottom sediments of the lower reaches of the Zeya and Selemdzha rivers are dominated by physically reworked rather than chemically reworked materials. It is suggested that the bottom sediments of the Zeya River downstream the mouth of the Selemdzha River were formed from material, which was supplied by the Selemdzha River and determined the main geochemical characteristics of the bottom sediments of the lower reaches of the Zeya River. This is presumably related to the fact that the upper reaches of the Selemdzha River is located mainly within the Mongol–Okhotsk fold belt, the complexes of which experienced intense tectonic shearing and brecciation. For this reason, the bottom sediments of the Selemdzha River are mainly dominated by physically reworked rather than by chemically reworked material.