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Natural environment of mid-latitude deserts of Central Asia is undergoing rapid changes. One of its elements is the relief. What needs to be particularly emphasized is its morphogenesis and landform evolution. In this study, a geomorphological research in the Ejina Basin (Inner Mongolia) is carried out with regard to identifying the main landforms and the contemporary geomorphic processes. We consider ancient and modern landforms as a unit and provide a general explanation for their evolution. Related environmental indications of existing landforms are discussed on the basis of climate geomorphology. Results show that the current basin is under the conditions favorable for the development and dominance of landforms originated from physical processes such as desiccation-deflation and aeolian. The landform system is characterized by its variable structure which is conditioned by specific hydrodynamics processes that existed during glaciations. It is suggested that landform patterns in Ejina are under the strong influence of rapid and/or intensive geomorphic processes. These signatures reflect the regional dynamics of landform evolution as characterized by a very effective integration of tectonic and climate-driven morphogenetic processes. Based on the present day climate data, we infer an obvious linkage of desert gorges and pediments in the basin to ancient humid phases, which provided high energy runoff for the formation of these landforms and were associated with erosional features under more humid and colder climate during the last glacial period. Desert plains and aeolian dunes in the central basin are the related products of contemporary climate. Clear evidences proving the landform inconsistency and landform instability in the Ejina are presented, indicating that the main geomorphic unit is experiencing transformation from alluvial plain to desert plain and then to aeolian dunes. However, the geomorphodiversity in the Ejina should be a compound result of complex surficial processes other than glaciation. Frost weathering, fluvial/alluvial action, desiccation-deflation and aeolian processes as well as climatic changes have played important roles. [ABSTRACT FROM AUTHOR]

Abstract: Chemical weathering is an integral part of the earth surface processes, whose spatial patterns and controlling factors on continental scale are still not fully understood. Highlands of the Asian continent have been shown having some of the highest observed rates of chemical weathering yet reported. However, the paucity of river gauge data in many of these terrains has limited determination of chemical weathering budget in a continental scale. A dataset of three large watersheds throughout northern Xinjiang in Central Asia is used to empirically identify chemical weathering regimes and interpret the underlying controlling factors. Detailed analysis of major ion ratios and a forward model of mass budget procedure are presented to distinguish the relative significances and contributions of silicate, carbonate weathering and evaporite dissolution. The analytical results show that carbonic acid is the most important weathering agent to the studied watersheds. Silicate weathering contributes, on average, ∼17.8% (molar basis) of total cations on a basin wide scale with an order of Zhungarer>Erlqis>Yili, indicating that silicate weathering, however, does not seem to be intense in the study basins. Evaporite dissolution, carbonate weathering and precipitation input contribute 43.6%, 29.7% and 8.9% of the total dissolved cations on average for the whole catchment, respectively. The three main morphological and hydrological units are reflected in water chemistry. Rivers from the montane areas (recharge area) of the three watersheds are very dilute, dominated by carbonate and silicate weathering, whereas the rivers of piedmont areas as well as the rivers of the sedimentary platform (runoff area) are dominated by carbonate weathering, and rivers of desert plain in the central Zhungarer basin (discharge area) are dominated by evaporite dissolution and are SO4 rich. This spatial pattern indicates that, beside lithology, runoff conditions have significant role on the regional chemical weathering regimes. Chemical weathering processes in the areas appear to be significantly climate controlled, displaying a tight correlation with runoff and aridity. Carbonate weathering are mostly influenced by runoff, which is higher in the mountainous part of the studied basins. The identification of chemical weathering regimes from our study confirmed the weathering potential and complexity of temperate watersheds in arid environment and that additional studies of these terrains are warranted. However, because the dominant weathering reactions in the sedimentary platform of northern Xinjiang are of carbonates and evaporites rather than silicate minerals, and the climatic factors have important role on the rock weathering regimes, we think that weathering at the arid temperate drainage system (Central Asia) is maybe not an important long-term sink for atmospheric CO2, if the future climate has no great change. [Copyright &y& Elsevier]