摘要:
采用岩性相和沉积体系的分析方法对茂县盆地三级阶地调查和研究,自下而上识别出河流沉积体系、扇三角洲沉积体系和风成沉积体系,是由Gms、Gm、Gg、Sh、Sg、Fl、Ls、Ps等岩性相组成。其主体是扇三角洲沉积体系,包含3部分:扇三角洲平原组合、扇三角洲前缘组合和前扇三角洲组合,剖面上体现了颗粒流-高密度浊流-碎屑流的变化。结合前人研究成果,扇三角洲沉积的发育与茂县古堰塞湖有关。茂县盆地在这一时期存在古堰塞湖,其成因可能与茂县-汶川断裂活动有关。根据岩性相和沉积体系的分析结果,探讨了茂县古堰塞湖的演化过程。风成黄土在本区广泛分布及其内部的5层古土壤的存在,说明在这一时期的气候主要是干冷,并且出现多次波动。
关键词:
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堰塞湖
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岩性相
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沉积体系
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岷江
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茂县
Abstract:
Studies of lithofacies and depositional systems had been carried out for the river terraces and the dammed paleolake in Maoxian basin on the upper reach of the Minjiang River. Based on field observation, the fluvial depositional system, fan-delta depositional system, and eolian depositional system were recognized in the terrace Ⅲ of the basin. They are composed of the lithofacies of Gms、Gm、Gg、Sh、Sg、Fl、Ls and Ps. The fan-delta depositional system could be further divided into 3 subfacies assemblages, namely, the pro-fan delta assemblage, fan delta front assemblage and fan delta plain assemblage. Changes from grain flow to gravity flow and then to clastic flow were observable in the section of fan-delta depositional system. Integrated with the previous research, it was suggested that the development of fan-delta depositional system may be linked to the dammed paleolake in the Maoxian basin. The appearance of the dammed lake during this period might be related to the activity of Maoxian-Wenchuan fault. Eolian loess and paleosoil were widely distributed in the area, suggesting that the climate was dry and cold then and frequently fluctuated in the area of Maoxian basin.
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