The geomorphology – sediment distribution – soil formation nexus on the northeastern Qinghai-Tibetan Plateau: Implications for landscape evolution

Abstract

The interactions between geomorphology, sediment distribution and soil development in alpine regions are poorly understood. In this study, we analyzed the spatial variations of different sediment types and corresponding soils in 15 pedosedimentary profiles across three major geomorphic units in an alpine ridge-valley basin of the Qilian Mountains, northeastern Qinghai-Tibetan Plateau. Particle size distribution was used to trace the sediment types. Inorganic and organic carbon concentrations were included as metrics of soil processes. Aeolian silts from both distant and proximal sources cover floodplains, hillslopes and some positions on alluvial fans, while the distribution of fluvial sediments and periglacial slope deposits are much more limited due to the coverage of loess. The soils vary in response to sediment types and climatic conditions under the influence of their geomorphic settings. The vertical distribution patterns of carbonates in soil profiles show considerable differences among different geomorphic units, reflecting their contrasting water balance and migration pathways. Soil organic carbon accumulates most extensively in aeolian silts with sufficient water supply. A special pedogenic soil horizon – the mattic epipedon is formed primarily in loessial sediments in Kobresia ecosystems. The complex entanglement of fine earths and massive grassroots make the mattic epipedon extremely resilient, which helps to preserve the soils and to shape the landscapes. By integrating geomorphology, sedimentology, ecology and pedology, the outcomes of this study promote the understanding of the evolution of typical landscapes and ecosystems of the northeastern Qinghai-Tibetan Plateau and many other periglacial settings.