| 江西象山地质公园丹霞地貌成景地层沉积环境分析 |
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| 引用本文： | 刘鑫,陈留勤,李馨敏,李余亮.江西象山地质公园丹霞地貌成景地层沉积环境分析[J].现代地质,2018,32(2):260. |
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| 作者姓名： | 刘鑫 陈留勤 李馨敏 李余亮 |
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| 作者单位： | (1东华理工大学 省部共建核资源与环境国家重点实验室培育基地，江西 南昌330013；
2东华理工大学 地球科学学院，江西 南昌330013) |
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| 基金项目： | 国家自然科学基金项目(41602113)；东华理工大学省部共建核资源与环境国家重点实验室培育基地开放基金(NRE1605)。 |
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| 摘 要： | 随着旅游地学的兴起和地学科普的需求，红层与丹霞地貌正在吸引着越来越多的关注。赣东北贵溪市象山地质公园发育以赤壁丹崖为特色的丹霞地貌景观，成景地层为上白垩统圭峰群河口组以砾岩为主的红色碎屑岩，冲刷侵蚀界面、粒序层理和交错层理等沉积构造发育，这为沉积环境分析提供了良好的判断标志。对该套成景地层进行厘米级实测，另外选择2处砾岩露头进行砾石统计以获取碎屑颗粒粒径、岩性、磨圆度和风化程度等信息。在实测厚度为40余米的地层柱状图上，识别出7种岩相类型，即正粒序砾岩、逆粒序砾岩、无沉积构造砾岩、平行层理砾岩、交错层理砾岩、聚集状砾岩、砂岩。砾石以中砾(2~5 cm)为主，磨圆度低，风化程度中等，成分以凝灰岩为主(58%~665%)，其次为石英、花岗岩、砂岩。砾石成分和砾向分析结果说明，盆地南部早白垩世凝灰岩提供了主要的碎屑物质。根据野外实测红层剖面和砾石统计分析，认为成景地层为冲积扇沉积体系的产物。河口组红层沉积时期，盆地边缘断层活跃，间歇性强降雨事件导致冲积扇朵叶上洪泛河流搬运的沉积物供应充足，最终在剖面上形成砾岩和砂岩频繁互层及其厚度横向不稳定的现象。在中国东南地区晚白垩世总体干燥的古气候背景下，河口组中河流作用主导的冲积扇沉积体系可能指示了古气候向湿润转变，降水增加，相对丰富的水系将粗碎屑搬运到盆地区发生沉积。
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| 关 键 词： | 丹霞地貌 沉积环境 冲积扇沉积体系 陆相红层 赣东北 |
Depositional Environments of the Bedrock of Danxia Landform in Xiangshan Geopark of Jiangxi Province,SE China |
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| LIU Xin,CHEN Liuqin,LI Xinmin,LI Yuliang.Depositional Environments of the Bedrock of Danxia Landform in Xiangshan Geopark of Jiangxi Province,SE China[J].Geoscience——Journal of Graduate School,China University of Geosciences,2018,32(2):260. |
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| Authors: | LIU Xin CHEN Liuqin LI Xinmin LI Yuliang |
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| Institution: | (1State Key Laboratory Breeding Base of Nuclear Resources and Environment, East China University of Technology, Nanchang，
Jiangxi330013, China; 2School of Earth Sciences, East China University of Technology, Nanchang，Jiangxi330013, China) |
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| Abstract: | Owing to the rise of tourism geoscience and the requirement of geoscience popularization, the research of redbeds and Danxia landform is attracting more and more attention. The Xiangshan Geopark of Guixi City in northeastern Jiangxi Province is featured by the prominent reddish cliffs. The bedrock of the Danxia landform is the conglomeratic strata of the Late Cretaceous Hekou Formation of the Guifeng Group, which is characterized by erosional bases, graded beddings and cross beddings. The sedimentary structures are useful to interpret depositional environments. A detailed centimeter scale outcrop section was measured to describe lithofacies. Moreover, two conglomerate outcrops were chosen to perform pebble counting. In the measured 40 meter thick stratigraphic column of the Hekou Formation, seven lithofacies were distinguished: normal graded conglomerate (facies A), inverse graded conglomerate (facies B), structureless conglomerate (facies C), parallel bedding conglomerate (facies D), cross bedding conglomerate (facies E), concentrated conglomerate (facies F), and sandstone (facies G). Clast sizes are mainly 2 cm to 5 cm, although it can range from 05 cm to 125 cm. Clasts are poorly rounded and moderately weathered. They are composed dominantly of tuff (58%-665%) with minor quartzite, granite, and sandstone, which is indicative of the dominant sediment derivation from the Early Cretaceous volcanic intrusive complex outcropped along the southern margin of the basin. Based on the measured section and pebble counting, the alluvial fan depositional system is envisaged for the formation of the redbeds of the study area. The sediment increments were produced by the combination of faulting along the basin margin with episodic strong rainfalls and transported by braided streams on the alluvial fan lobes. As a result, the frequent interstratification of the conglomerate and sandstone beds, erosions, prevalent fining upward units were preserved in the outcrops. In addition, under an overall arid climate regime during Late Cretaceous in Southeastern China, the stream dominated alluvial fan systems were indicative of a climate change towards greater humidity which possibly resulted in abundant streams transporting coarse sediments to the basin area. |
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| Keywords: | Danxia landform depositional environment alluvial fan depositional system continental redbed Northeastern Jiangxi Province |
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