Characteristics of Quartz Grains of the Xiashu Loess in Zhoujiashan Nanjing and Its Provenance Significance

Key words: 
• quartz grain size /
• surface microstructive /
• provenance /
• Xiashu Loess /
• Zhoujianshan

Abstract: The genesis and source of the Xiashu Loess has always been a hotspot of academic research. We have analyzed the grain size of quartz and it's surface microstructive of the Xiashu Loess in Zhoujiashan Nanjing. The results show that silt fraction of quartz grains(5~50 μm) accounts for absolute advantage. The content of the corase silt fraction of quartz grains(10~50 μm) occupies 65.4%. The content of <30 μm component occupies 62.98%, while the content of <20 μm component occupies 42.76%. There is an opposite changes of the content in section between clay fraction and coarse silt fraction. The Xiashu Loess in Zhoujiashan Nanjing is similar to typical Northern Loess in China with the particle size distribution and cumulative curves. Overall, it presents the characteristics of very fine skewness, poorly sorting, leptokurtic and asymmetrical bi-modal curve in quartz grain size parameters. Grade-standard deviation curves present the distribution of "twin peak". Two obvious peaks in standard deviation is nearly 7.962 1 μm and 39.905 2 μm. The scope of the grain size fraction, corresponding to the two peaks, present to 0.399 1~15.886 6 μm and 15.886 6~112.468 3 μm, respectively. The surface shapes of quartz grains are mainly sub-angular. Surface mechanical structures not only have the characteristics of eolian features such as rich dish-shaped pits, curve ridge, parallel joint surface, textured structure and so on, but also slightly show the underwater environment characteristic as conchoidal breakage fractures, underwater ground surface and V-shaped pits. Meanwhile, it is different to the surface microstructive between 5~30 μm component and 30~50 μm component. Finally, our analysis has found that the Xiashu Loess in Zhoujiashan Nanjing belongs to the typical eolian-formation debris. It is probably a high degree of mixture with multiple sources. Our study has an important theoretical significance to understand the area dust transport mechanism.