| 江西石城国家地质公园龟裂地貌特征及成因分析 |
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| 关键词:polygonal cracks red sandstones case hardening Danxia landscape Shicheng National Geopark |
| 基金项目:国家自然科学基金项目(编号: 41772197; 41962009; 41761002);东华理工大学研究生创新项目(编号: DHYC-201803) |
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| Characteristics and Origin of Polygonal Cracks in the Shicheng National Geopark of Jiangxi Province |
| Polygonal cracks in the Shicheng National Geopark of Jiangxi Province are generally observed along the red sandstone surfaces of the Late Cretaceous Hekou Formation. They are characterized by various vivid shapes and have formed many pictorial landforms, such as Guishoushi (huge turtle-like rock), Songguoshi (huge pine cone-like rock), and Xianrenlitian (rectangular polygons). However, microscopic studies of these polygonal cracks are insufficient. In consequence, their formation mechanism has been yet poorly understood. In this study, a compass was used to measure the orientations of the cracks in the field. Sandstone samples were collected for experimental analysis by a polarizing microscope and scanning electron microscope. The results show that the polygonal cracks are mainly developed in thick-bedded fine-grained sandstones with relatively uniform granules, which can be observed along the sandstone beddings or other exposed rock surfaces, and generally extend downwards for less than 15 cm. Under the polarizing microscope, the particles of the sandstone samples are mostly sub-angular to sub-rounded and well-sorted. The interstitial material dominantly consists of calcite cement. Under a scanning electron microscope, the grains are loosely cemented, and the pores and cracks on the surface of quartz and feldspar particles are commonly observed. Based on similar studies both in China and abroad, it is held that the lithology should be fundamental for the development of polygonal cracks. The rose diagrams of the cracking show that the regional fault systems control the formation of some cracks to some extent, but this is not the only mechanism. Owing to the precipitation of silicon, iron and manganese oxides, a thin layer of crust is formed within the surface of the sandstones during the weathering processes. The crust would be broken to form tiny cracks after the stress is stretched. These small cracks would become enlarged particularly because of the water flows along them. Then, the cracking features are formed. Finally, a four-stage evolution model of cracking landforms is proposed. |
| ZHANG Peng-qiong,CHEN Liu-qin,GUO Fu-sheng,PAN Zhi-xin,LIU Xin.2020.Characteristics and Origin of Polygonal Cracks in the Shicheng National Geopark of Jiangxi Province[J].Acta Geoscientica Sinica,41(1):117-126. |
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