Abstract:

At least 10% of the continental surface in the Northern-Hemisphere —particularly in western and central Eurasia—is covered by eolian mineral dust and sandy deposits, many of which are mapped as loess. The origin and spatial pattern of these sediments reflects past (paleo-)environmental conditions and are an important edaphic factor for eco-zone evolution.
Here, we present an updated conceptual model based on the European loess facies classification (Lehmkuhl et al., 2021), which distinguishes three climate-controlled modes of loess formation: Mode 1: periglacial/tundra loess (cold, moist climate; tundra/alpine vegetation; silt-dominated deposits). Mode 2: temperate-subtropical loess (moderate temperature and precipitation; forest/steppe vegetation; mixed silt-/fine-sand fractions). Mode 3: desert-margin loess (warm, arid climate; xeric shrubland/desert vegetation; sand-rich deposits sourced from dry riverbeds and exposed lacustrine surfaces). Continuous silt-dominated, typical loess primarily forms in the transitional zones between these modes.
Applying the model to the Chinese Loess Plateau reveals a gradient in grain-size from clay-rich to silty loess in the humid southern areas to increasingly sandy loess toward the semi-arid and arid north-west regions. Similar patterns occur in Eastern Europe and Central Asia (e.g., the surroundings of the Sea of Azov, the Caspian Lowlands and the deserts towards the east). Periglacial loess (Mode 1) dominates in high mountain regions and in northern Mongolia and Siberia, whereas desert-margin loess (Mode 3) is found in the arid regions of Central Asia. Humid highlands, such as the eastern margin of the Tibetan Plateau, lack loess almost entirely.
The model provides a unified framework for interpreting loess distribution across climatic, vegetational, and topographic gradients in Eurasia.