Distributional Characteristics of Carbonate and Carbon Isotopic Compositions in Different Grainsize Fractions and Their Implications for Dust Provenance

Key words: 
• carbonate

Abstract: Carbonate and its carbon isotopes have the potential for distinguishing dust provenance, and but the differences for carbonate and carbon isotopes in different grainsize fractions significantly affect accuracy for identifying dust provenance. Therefore, the study for distribution characteristic of carbonate and carbon isotopes in different grainsize fractions is theory base of dust provenance trace with use of carbonate and carbon isotopes. Samples of sandy land have be collected from horqin sandy land and dumeng sandy land in songnen plain, at one time, samples also are collected from city road loose bare soils. These samples are separated into five different grain size fractions, i. e. bulk sample, >63 μm, 63~30 μm, 30~11 μm, and <11 μm. Then, carbonate volume and carbon isotopic compositions of these samples are measured, respectively. The results show that the varied range of carbonate volume of different grain size fractions in horqin sandy land and dumeng sandy land are fairly minor, although carbonate volume of most samples raise with decreasing grain size, but relations between carbonate volume and grain size are not only a relations that carbonate volume becomes high with decreasing grain size, but also have other much complex relations. The carbonate volume of all road loose bare soils increases with decreasing grain size, and might be caused by join of fine grainsized pollutants such as construction dust. The carbonate volumes of full fractions are similar to that of the >63 μm fraction. It is believed that the carbonate volume of eolian sand and sandland samples undergoing transform of violent pedogenesis decreases with decreasing size of sample particles. The varied scopes of carbon isotopic compositions of different grain size fractions of most samples in dumeng sandy land and road loose bare soils and all samples in Horqin sandy land are fairly minor, and express the characteristics of increase with decreasing grain size, but the varied changes are very slight. The carbonate volumes are not a good dust source region tracer indicator of distinguishing between dumeng sandy land and Horqin sandy land because of not very obvious regional differences of carbonate volumes between dumeng sandy land and Horqin sandy land, and of variations of carbonate volumes in different grain size fractions that is much higher than the different value of carbonate volumes between dumeng sandy land and horqin sandly and. However, there exist the obvious differences between carbon isotopic compositions in dumeng sandy land and Horqin sandy land (63~30 μm grain fraction, specifically), and the differences of δ13C compositions in different grain size fractions are very slight, showing carbonate carbon isotopic compositions in dust fallouts is a better tracing index for indicating eolian dust provenance than carbonate contents. However, the diversity of carbonate carbon isotope compositions in different grainsize fractions maybe increase with increasing distance of dust source regions in west desert and sandy land in China to dust deposit regions, which increase its complexity for identifying dust provenance.