CSCO_3 CYCLES IN SALAWUSU RIVER BASINSINCE 150KA B.P.

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CaCO3 cycles in salawusu river basin since 150ka B.P.

ABSTRACT: This paper, with Milanggouwan stratigraphic section as a typical section of the Salawusu River Basin, explores the relation between CaCO3 content distribution and climate change since 150 ka B. P. and concludes that: 1) The low-high changes of CaCO3 content in the section has a remarkable corresponding relation with the sedimentary cycles of ancient aeolian sand and overlying fluviolacustrine facies or palaeosols. 2) CaCO3 distribution in aeolian sand is relatively meagre, ranging from 0. 8% - 7. 18%, or on an average 2. 50% but relatively enriches in the fluviolacustrine faceis and palaeosols, ranging from 2. 20% - 14. 9% , or on an average 5. 74%. This implies that they have different climatic backgrounds. The former was the product of erosion, transport and deposition by wind under arid and cold climatic conditions, whereas the latter was related to its special low-lying geomorphic position between the Ordos Plateau and Loess Plateau and warm-humid climatic environment. When the climatic became warm and humid, fluviolacustrine and swamp facies developed, soil-forming action strengthened, and low-lying catchment condition was favorable to CaCO3 accumulation. 3) The basic cause responsible for the multicycle of CaCO3 migration and accumulation in the Milanggouwan section may be the multiple alterations of winter and summer monsoons over the Mu Us Desert under the influences of climatic fluctuation of glacial and interglacial periods in the Northern Hemisphere since 150ka B. P. .